Filament shield for sealed headlamp and mounting method therefor
BACKGROUND OF THE INVENTION 
     Modern automotive headlamps require precise positioning of the filament with respect to the reflector. In addition, they require precise positioning of a filament shield forward, aft and to the sides of the filament to prevent the forwards aft and sideways projection of light rays directly from the filament. In particular, the embodiment described prevents the utilization of light rays from approximately the lower half of the filament. 
     The prior art fails to teach a method of mounting both filament and filament shield in a precise manner while requiring only normal handling of the parts during assembly. 
     SUMMARY OF THE INVENTION 
     The instant invention teaches a headlamp filament and shield, and the method of assembling same which enables precise positioning of both filament and shield within the reflector of the headlamp envelope. 
     The filament and its shield are first welded together into a rigid subassembly. The filament/shield subassembly is welded as a unit to support and power-source pins within the headlamp. A portion of the filament shield, previously producing an electrical short circuit across the filament is cut away after the subassembly is securely aligned and welded in place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic view of a headlamp containing the filament shield and lamp filament of the present invention. 
     FIG. 2 shows the required illumination and blocking of the headlamp reflector. 
     FIG. 3 shows a top view of the headlamp shield. 
     FIG. 4 shows the lamp filament. 
     FIG. 5 shows the filament shield and filament in a unitary subassembly. 
     FIG. 6 shows a cross-sectional view of the filament shield and filament taken along 6--6 of FIG. 5. 
     FIG. 7 shows the shield/filament subassembly mounted in a headlamp reflector. 
     FIG. 8 shows the filament and shield installed and trimmed in its final assembled condition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the arrangement of the low-beam lamp filament in a European-type headlamp shown generally at 10. A cylindrical spiral lamp filament 12 is located with the axis of the cylindrical lamp filament 12 approximately on the axis of the paraboloid lamp reflector 14. The specifications for such lamps require that the low-beam filament 12 be prevented from illuminating certain portions of the lamp reflector 14. In addition, the specifications require that axial and near-axial forward radiation directly from the filament 12 be blocked. This control of directional illumination is accomplished using a shield 15 which partially encloses the filament 12. 
     An aft shield 16, interposed between the filament 12 and the reflector 14 blocks direct rearward illumination of the reflector 14 by the filament 12. The shape of this blockage will be described in later paragraphs. A forward shield 18, larger than the aft shield, is located forward of the filament 12. The forward shield 18 blocks forward radiation directly from the filament 12. A lower shield 20 blocks illumination of the bottom and sides of the reflector in a predetermined pattern. The remaining illumination from the filament 12, after reflection from the reflector 14, is directed below the axis of the lamp reflector 14 as required by the specifications of this type of lamp 10. 
     FIG. 2 shows the desired illumination pattern of the reflector 14. The stippled portion 22 describes the area required to be blocked from illumination by the filament. The plain portion 24 describes the illuminated area. In addition to blockage of the lower 165° of the reflector 14, the blocked portion 22 also includes a semicircular central blocked portion 26 concentric with the paraboloid axis. 
     A top view of the shield 15 is shown in FIG. 3. The forward direction is downward in FIG. 3. The shield 15 contains a concavity 28 within which the filament 12 is suspended. An approximately rectangular mounting plate 30 extends outward, toward the right in the drawing, from the concavity 28. Two stiffening corrugations 32, 32a in the mounting plate 30 extend outward from the concavity 28 to a mounting flange 34. 
     A flat flange 36 is connected to the left side of the shield 15 in the drawing. A depression 38 is provided near the forward end of the flat flange 36, to provide clearance for one of the filament 12 legs as will be described later. A bump 40 is positioned in the rear of the flat flange 36 to provide an electrical and mechanical connection point for the filament 12. 
     A forward shield 42 prevents the forward projection of light from the filament 12. 
     A J-shaped projection 44 projects from adjacent the forward end of the flat flange 36. The J-shaped projection 44 has a long leg 46, a short leg 48, and a base 50. 
     The filament 12 is shown in FIG. 4. The filament 12 is of the type shown as a Sleeper-Hartley filament. The Sleeper-Hartley filament consists of a cylindrical coil of filament wire 52 and two parallel legs 54, 56. The filament legs 54, 56 in this embodiment of the present invention are of unequal length. The long filament leg 54 is longer than the short filament leg 56. The cylindrical coil of filament wire 52 contains an integral number of turns plus 1/2 turn. Thus the two legs 54, 56 emerge from the coil 52 parallel to each other on the same side of the axis of the coil 52 but separated by the diameter of the coil. As shown in the figure, the long filament leg 54 projects toward the left from the bottom of the coil 52 whereas the short filament leg 56 projects toward the left from the top of the coil 52. 
     FIG. 5 shows a preassembled subassembly in which the filament 12 is preassembled into the filament shield 15. The long filament leg 54 passes through the depression 38 without making mechanical or electrical contact at this point and makes contact with the short leg 48 of the J-shaped projection 44. The long filament leg 54 is welded to the short leg 48 of the J-shaped projection 44 at their point of contact 58. The short filament leg 56 passes over the flat flange 36 and makes contact with the bump 40. The short filament leg 56 and the bump 40 are welded at their point of contact 60. 
     When preassembled in the fashion described in preceding paragraphs, the filament shield 15 and filament 12 form a rugged subassembly adapted to handling in further manufacturing processes without losing the required spatial relationships between them. Note that at this stage of preassembly, the filament shield provides a dead electrical short across the legs 54, 56 of the filament 12. 
     The cross-sectional view in FIG. 6 taken along line 6--6 in FIG. 5 illustrates the relative positioning of the elements of the subassembly. Mounting flange 34 at the outer end of the mounting plate 30 is seen to contain an S-shaped curve contaiing an inner concave angle 62 and an outer concave angle 64. The outer concave angle 64 is used for precise positioning of the subassembly within the headlamp reflector as will be described later. The stiffening corrugation 32a and 32 (behind 32a) contribute rigidity to the mounting plate 30 in order that the assembly may resist motion under normal road use. 
     The long filament leg 54 is shown, at the end of the filament 12 nearest the viewer, passing through the depression 38 and making contact with the short leg of the J 48. The long leg of the J 46 is bent at the point it joins the flat flange 36 in order to translate the short leg of the J 46 to the level required to make collinear contact with the emerging long filament leg 54. 
     The short filament leg 56, at the end of the filament 12 farthest from the viewer, makes contact with the bump 40. 
     The aft shield 16 is shown to contain an upper semicircular part 66 and a lower part 68. This shape of the shield 16 provides the correct blocking pattern to provide the specified pattern of reflector illumination as previously shown in FIG. 2. 
     The installation of the subassembly in the headlamp begins with the arrangement shown in FIG. 7. A first mounting pin 70, passing sealably through the lamp reflector 14, provides both mechanical support and electrical supply to the subassembly. A second mounting pin 72 provides an initial alignment bearing and subsequent electrical supply to the subassembly. The outer concave angle 64, running the entire length of the mounting flange 34 is fitted against the first mounting pin 70. The shiled 15 is rotated about its bearing line on the first mounting pin 70 until the base of the J 50 comes to bear against the second mounting pin 72. When positioned in this way, the filament/shield subassembly is in precise alignment between its own elements and relative to the lamp reflector 14. The mounting flange 34 and first mounting pin 70 are welded together along their line of contact. The base of the J 50 and the second mounting pin 72 are welded together at their contact. The long leg of the J 46 is thereupon cut away to remove the electrical short circuit previously existing across the filament 12. FIG. 8 shows the resulting configuration. Mechanical support and one electrical connection to the filament 12 is provided through the first mounting pin 70, the body of the filament shield 15, and the bump 40 to the short filament leg 56. The strength and rigidity of the first mounting pin 70 is sufficient by itself to support the filament shield 15 and filament 12 against mechanical movement. The second mounting pin 72 merely provides the second electrical connection to the filament 12 through the remaining portions of the J-shaped projection 44 and the long filament leg 54. The second mounting pin 72 also provides mechanical support for one end of the filament 12.