Abstract:
The present invention provides a headlamp for a vehicle wherein a reflector is different in focal position of a paraboloidal surface between an upper surface and a lower surface thereof, a focal point on the lower surface side is formed to be positioned forwardly more than a length of a sub-filament from a focal point on the upper surface side, and the sub-filament is positioned between both the focal points to thereby efficiently utilize luminescense and obtain a light distribution pattern of high luminous intensity.

Description:
This application is a continuation of application Ser. No. 634,877, filed July 26, 1984, now abandoned. 
    
    
     SUMMARY OF THE INVENTION 
     The present invention relates to a headlamp for a vehicle in which a main beam and a sub-beam may be switched. 
     DESCRIPTION OF THE PRIOR ART 
     An example of a filament arrangement of a conventional headlamp for a vehicle is shown in FIGS. 1 and 2. FIG. 1 shows the case wherein forwardly directed main filament and sub-filament 3 (the main filament being positioned behind the sub-filament 3) are successively arranged on a rotational shaft of a paraboloidal surface of a reflector 1, and a shield plate 4 is arranged under the sub-filament 3. A light image of the sub-beam assumes an approximately semi-circle by use of about a half portion except a portion marked with oblique lines of the reflector as shown in FIG. 3 (a), and a light image of the main beam assumes a circle by use the whole reflector as shown in FIG. 3 (b). 
     FIG. 2 shows the case wherein a main filament 2 is arranged on a center axis of the reflector 1, and a sub-filament 3 is arranged thereabove. A light image of the main beam assumes a laterally extending elliptical shape as shown in FIG. 4 (b), and a light image of the sub-beam assumes a shape in which an ellipse is inflated in one direction of a short axis thereof as shown in FIG. 4 (a). 
     As will be apparent from the light images, in the filament arrangement of FIG. 1, the sub-beam is merely possible to utilize light about half of the reflector, and therefore, the rate of utilization is bad. 
     On the other hand, in the filament arrangement of of FIG. 2, the light image of the sub-beam tends to be spread resulting in possible short of intensity of illumination, and in addition, a gap between the main-filament 2 and the sub-filament 3 should be more than a given value. Therefore, if the center of the light image is positioned much lower than the center point of the reflector 1, correction becomes difficult to make, and lateral light is weak. If combined with a laterally extending reflector, the degree of utilization of light is low and therefore, selection of a reflector has to made carefully. 
     OBJECT OF THE INVENTION 
     In view of the foregoing, the present invention has its object to provide a headlamp for a vehicle wherein a reflector is different in focal position of a paraboloidal surface between an upper surface and a lower surface thereof, a focal point on the lower surface side is formed to be positioned forwardly more than a length of a sub-filament from a focal point on the upper surface side, and the sub-filament is positioned between both the focal points to thereby efficiently utilize luminescense and obtain a light distribution pattern of high luminous intensity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are respectively front views showing an example of a filament arrangement of a conventional headlamp for a vehicle; 
     FIGS. 3 (a) and (b) and FIGS. 4 (a) and (b) show patterns of a sub-beam and a main beam in the filament arrangements of FIGS. 1 and 2; 
     FIGS. 5 and 6 are respectively a longitudinal sectional view and a front view showing one embodiment of the present invention; 
     FIGS. 7 (a) and (b) show patterns of the sub-beam and main beam in the aforesaid embodiment; and 
     FIGS. 8 and 9 show patterns which can be realized by the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 5 and 6 show one embodiment of the present invention. Reference numeral 11 denotes a reflector, 12 a main filament, and 13 a sub-filament. 
     The reflector 11 has a paraboloidal surface (reflecting surfaces A, B) of a focal length F 1 , and a paraboloidal surface (reflecting surfaces C, D) of a focal length F 2 . A length between focal points f 1 , f 2  (f 2  is positioned frontwardly of f 1 ) has a value of a length l of the sub-filament 13 plus 0-1.0 mm. A boundary between both the paraboloidal surfaces is a horizontal line intersecting a rotational axis Z of the paraboloidal surface of the reflector. 
     The sub-filament 13 is arranged between both the focal points f 1 , f 2  on the rotational axis Z of the paraboloidal surface of the reflector 11, and the main filament 12 is arranged thereunder by dimension S (1.0-3.0 mm) in parallel to the sub-filament 13. In this case, the main filament 12 is formed to be longer than the sub-filament 13 by l&#34; or l&#39; (0.5-1.5 mm), projecting rearwardly (reflector side) by l&#34;-l&#34;+L/2 or forwardly (lens side) by l&#39;-l&#39;+L/2 (where L: length of the main filament). It will be noted that both the filaments are manufactured as a bulb in the aforesaid positional relation. 
     With the above-described construction, light from the sub-filament 13 will be light externally of the focal point f 1  with respect to the reflecting surfaces A, B of the focal length F 1  and focal point f 1 , and when the light is illuminated on the reflecting surfaces A, B, an image of light is formed under the horizontal line (center line) intersecting the axis Z as shown in FIG. 7 (a). The afore-said light will be light within the focal point with respect to the reflecting surfaces C, D of the focal length F 2  and focal point f 2 , and an image of light is formed at the same position as the reflecting surfaces A, B. 
     On the other hand, the main filament 12 is arranged parallel to the sub-filament 13 with a gap of dimension S (1.0-3.0 mm), and an image of light (contour m 1  of FIG. 7 (b)) is formed in a portion of the same length as the sub-filament 13 according to the same principle as the sub-beam. However, light generated from the portion of l&#34; is illuminated as light within the focal point with respect to the reflecting surfaces A, B of the focal length F 1 , and an image of light (contour m 2  of FIG. 7 (b)) is formed above the center line. Light in the portion of dimension l&#34; will be light within the focal point with respect to the reflecting surfaces C, D of the focal length F 2  and has the same directivity as the portion of dimension l and therefore, a light image of contour m 3  of FIG. 7 (b) is obtained. 
     In case of the main beam, even if it is arranged while being projected frontwardly through l&#39;, the directivity of light is merely changed in the reflecting surfaces A, B and C, D, and the combined light image is the same as the case of dimension l&#34;. Also, an axis of a reflecting mirror of any of the reflecting surfaces A, B, C and D may be varied to vary the light image stepwise as shown in FIG. 8. This stepwise light image will be a light image convenient to find a center axis of the illuminating lamp where the illuminating lamp is mounted on the vehicle. Moreover, by varying the dimension S (gap in filament) of FIG. 6 or by varying the amount of movement T of the sub-filament 13 to right or left, it is possible not to impart dazzling to a facing vehicle and possible to preferentially brighten the rightside or leftside. 
     As described above, in the present invention, the sub-beam is formed by improvement in construction of the reflecting surface of the reflector and by optical consideration of arrangement of the filaments, and therefore, light is effectively utilized and a pattern of sufficient light intensity is obtained. Moreover, the minimum light of the main beam is used to illuminate the sky, and the remaining light is sued to illuminate the road surface. Therefore, the road surface can be illuminated brightly, contributing safety driving. In the type shown in FIG. 2 wherein both filaments are arranged in parallel up and down, there is a limitation in reduction of a switching width between the main beam and the sub-beam in terms of arrangement of filaments, and the sub-beam has a disadvantage in that it illuminates a short-distance portion as compared with the sub-beam of the type shown in FIG. 1 which employs the longitudinal arrangement. However, even if both filaments are likewise arranged in parallel up and down, a portion in an adequate range can be illuminated with high light-intensity. Moreover, various light images may be realized by adjustment of an axis of the reflecting mirror, and the sub-beam may be illuminated against a portion remotely located without imparting dazzling to the facing vehicle. Furthermore, by effective utilization of luminescense, there provides the advantage in that the vertical light dimension employed in the type in which the filaments are longitudinally arranged may be reduced.