Abstract:
A vehicular headlamp of a type having a lighting circuit unit mounted on an outer surface of a bottom wall of the lamp body in which failure of the seal between the lamp body and a front lens mounted thereon is prevented. A bottom wall extension portion is formed at a rear end portion of a bottom wall of the lamp body, extending rearward beyond a bulb replacement opening formed in a rear wall of the lamp body. This structure provides sufficient rigidity for the rear end portion of the bottom wall, which otherwise would have insufficient rigidity because of its location adjacent the bulb replace opening. Therefore, the bottom wall is protected from deflection deformation due to the weight of the lighting circuit unit. As a result, the front end opening of the lamp body is protected from deformation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a vehicular headlamp having a discharge bulb as its light source. 
     BACKGROUND OF THE INVENTION 
     There has been a recent trend in vehicular headlamps toward adopting discharge bulbs that can emit light of high intensity as the light source bulb. 
     A vehicular headlamp equipped with a discharge bulb of this type requires a lighting circuit unit to ignite the discharge bulb. Referring to FIG. 6, a lighting circuit unit  102  is in many cases mounted on an outer surface of a bottom wall  104   a  of a lamp body  104 . 
     Because of a relatively heavy weight associated with the lighting circuit unit  102 , deflection deformation tends to occur in the bottom wall  104   a  of the lamp body  104  when the lighting circuit unit  102  is mounted on the outer surface of the bottom wall  104   a . Moreover, a cord insertion opening  104   b , used for passing a power feeding cord  108  connecting the lighting circuit unit  102  to a discharge bulb  106 , is formed in the bottom wall  104   a . A bulb replacement opening  104   d  for allowing replacement of the discharge bulb  106  is formed in a rear wall  104   c  of the lamp body  104 . These arrangements result in insufficient rigidity in the rear end portion of the bottom wall  104   a . This may also result in deflection deformation of the bottom wall  104   a  due to the weight of the lighting circuit unit  102 . 
     Deflection deformation in the bottom wall  104   a  can also eventually result in deformation in a front end opening  104   e  of the lamp body  104 , thus leading to failure in the seal between the lamp body  104  and a front lens  110 . 
     SUMMARY OF THE INVENTION 
     In view of the foregoing situation, it is an object of the present invention to provide a vehicular headlamp in which a lighting circuit unit is mounted on the outer surface of a bottom wall of a lamp body and yet which does not induce failure in the seal between the lamp body and front lens. 
     The present invention achieves the above object by forming a bottom wall extension portion in a bottom wall of a lamp body. 
     More specifically, a vehicular headlamp of the present invention includes a reflector supporting a discharge bulb housed in a lamp chamber defined by a lamp body, a front lens fitted in an opening at a front end of the lamp body, and a lighting circuit unit for igniting the discharge bulb installed on an outer surface of a bottom wall of the lamp body, and in which a bulb replacement opening for replacing the discharge bulb is formed in a rear wall of the lamp body, and a cord insertion opening, through which a power feeding cord connecting the lighting circuit unit to the discharge bulb passes, is formed in the bottom wall of the lamp body. The vehicular headlamp of the invention is characterized in that a bottom wall extension portion extending rearward beyond the bulb replacement opening is formed at a rear end portion of the bottom wall of the lamp body. 
     The lighting circuit unit may be constructed so as to be mounted directly, or indirectly via a bracket, unit cover, or other means, on the outer surface of the bottom wall. 
     The shape of the bottom wall extension portion is not limited so long as it extends rearward beyond the bulb replacement opening. 
     As described above, the vehicular headlamp according to the present invention has, at the rear end portion of the bottom wall thereof, a bottom wall extension portion which extends rearward beyond the bulb replacement opening, even though the bulb replacement opening is formed in the rear wall of the lamp body and the lighting circuit unit is mounted on the outer surface of the bottom wall of the lamp body, thus providing operational effects as discussed in detail below. 
     Namely, sufficient rigidity cannot be obtained from the rear end portion of the bottom wall of the lamp body alone since it is adjacent to the bulb replacement opening formed in the rear wall of the lamp body. By providing the bottom wall extension portion according to the present invention it becomes possible to obtain sufficient rigidity for the rear end portion of the bottom wall. This prevents the bottom wall from developing deflection deformation due to the weight of the lighting circuit unit, which in turn prevents deformation of the front end opening in the lamp body. Accordingly, failure of the seal between the lamp body and the front lens is prevented. 
     Forming the bottom wall extension portion on the bottom wall of the lamp body results in an area of the outer surface of the bottom wall extending rearward. This allows the lighting circuit unit to be mounted at a position further rearward on the outer surface of the bottom wall than would otherwise be possible. This arrangement of the lighting circuit unit permits the mounting of the lighting circuit unit on the bottom wall so that it crosses the rear wall, which prevents deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should some deflection deformation occur, the front end opening is not influenced by such deformation, thus suppressing failure in the seal between the lamp body and the front lens. 
     In the vehicular headlamp of the invention equipped with a lighting circuit unit mounted on the outer surface of the bottom wall of the lamp body, failure of the seal between the lamp body and the front lens is effectively prevented. 
     The aforedescribed structure can further be provided with a plurality of reinforcement ribs extending rearward from the rear wall of the lamp body and which are formed on a top surface of the bottom wall extension portion. With the reinforcement ribs the rigidity of the lamp body is enhanced in the area extending from the rear wall to the bottom wall extension portion. This structure is effective to suppress deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should any deflection deformation nevertheless occur, the front end opening is not subjected to such deformation, thus preventing failure of the seal between the lamp body and the front lens further effectively. 
     If the bottom wall extension portion in the aforementioned structure is formed as a folded-back portion having substantially a U-shape in cross section, the rigidity of the bottom wall extension portion is enhanced. This structure is effective in reducing deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should some deflection deformation nevertheless occur, the front end opening is not subjected to such deformation, thus preventing failure of the seal between the lamp body and the front lens more effectively. 
     Assuming that a unit cover for covering the lighting circuit unit is mounted on the outer surface of the bottom wall of the lamp body in the aforementioned structure, and the part of the unit cover mounting sealing portion on the bottom wall, which is located rearward of the lighting circuit unit, is formed on the bottom surface of a bottom wall extension portion, which extends rearward from the rear end portion of the bottom wall. As a result, the unit cover mounting sealing portion is protected from deformation, which in turn contributes to obtaining and maintaining a good seal between the unit cover and lamp body. 
     In this case, the unit cover may be installed separately from the lighting circuit unit mounted on the outer surface of the bottom wall. It may be installed together with the lighting circuit unit on the outer surface of the bottom wall. It may also be assembled with the lighting circuit unit preliminarily so as to be mounted on the outer surface of the bottom wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view showing a vehicular headlamp according to a preferred embodiment of the present invention. 
     FIG. 2 is a cross-sectional view taken along a line II—II in FIG.  1 . 
     FIG. 3 is a perspective view in a direction III indicated in FIG.  2 . 
     FIG. 4 is a sectional side elevational view showing a modified example of the embodiment of FIGS. 1-3. 
     FIG. 5 is a perspective view in the direction of an arrow V in FIG.  4 . 
     FIG. 6 is a view similar to FIG. 2 but showing a conventional vehicular headlamp. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described referring to the drawings. 
     FIG. 1 is a front view showing the vehicular headlamp according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II—II in FIG.  1 . FIG. 3 is a perspective view in the direction of an arrow III shown in FIG.  2 . 
     As shown in these drawings, a vehicular headlamp  10  according to the present embodiment is a four-lamp system in which a pair of left and right reflector units  16 ,  18  is housed in a lamp chamber defined by a lamp body  12  and a front lens  14  fitted in an opening  12   a  at a front end of the lamp body  12 , and the reflector units are mounted in such a manner that they can be adjustably tilted in vertical and horizontal directions by respective aiming mechanisms (not shown in the drawings). An extension panel  44  is provided forward of the two reflector units  16 ,  18 . 
     The front lens  14  is a transparent lens, and thus the two reflector units  16 ,  18  provide the light distribution control function for the headlamp. 
     The reflector unit  16 , which is used for the main (high) beam, is formed of a reflector  20  having a reflecting surface  20   a  on which a plurality of reflecting elements are formed and a halogen bulb  22  mounted on the optical axis Ax 1  of the reflector  20 . By incorporating the diffusion or deflection function into the reflector  20  it is ensured that the output beam will form the desired main beam light distribution pattern in the forward direction. 
     The reflector unit  18  is used for the sub (low) beam. It is formed of a reflector  24  having a reflecting surface  24   a  on which a plurality of reflecting elements are formed, a discharge bulb  26  mounted on the optical axis Ax 2  of the reflector  24 , and a shade  28  fitted on the reflector  24  so as to cover the discharge bulb  26  over a predetermined angular range. As in the previously described case, by incorporating the diffusion or deflection function into the reflector  20  it is ensured that the output beam will form the desired main beam light distribution pattern in the forward direction. 
     A lens sealing groove  12   b  for mounting the front lens  14  is formed around the entire circumference of the front end opening  12   a  of the lamp body  12 . A bulb replacement opening  12   d  for permitting replacement of the discharge bulb  26  is formed in a rear wall  12   c  located to the rear of the reflector unit  18  in the lamp body  12 . A back cover  46  is fitted into the bulb replacement opening  12   d.    
     Furthermore, a bottom wall extension portion  12   f  is formed at a rear end portion of a bottom wall  12   e  located below the reflector unit  18  in the lamp body  12 , extending further rearward than the bulb replacement opening  12   d . The bottom wall extension portion  12   f  is formed with a plate-like shape so as to directly extend the bottom wall  12   e  rearward. In addition, seven reinforcement ribs  12   g  that extend rearward from the rear wall  12   c  are formed on a top surface of the bottom wall extension portion  12   f . The height of a base edge portion of each of these reinforcement ribs  12   g  is set so as to run along the circular shape of the bulb replacement opening  12   d . That is, the height of the base edge portion of centrally located reinforcement ribs  12   g  is lower than that of the reinforcement ribs  12   g  located on both left and right edges. 
     As the discharge bulb  26  requires high voltage for ignition, it is connected to a lighting circuit unit  34  via a bulb socket  30  and a power feeding cord (high voltage cord)  32 . The lighting circuit unit  34  is provided with a starting circuit and a stabilizing circuit, both housed in a lighting circuit case. The case is fitted on the outer surface on a rear end side of the bottom wall  12   e  of the lamp body  12 . A cord insertion opening  12   h , through which the power feeding cord  32  passes, is formed in the rear portion of the bottom wall  12   e.    
     The top end surface of the lighting circuit unit  34  is abutted against the bottom wall  12   e  of the lamp body  12 , and a tab  34   a  formed on the rear end surface of the lighting circuit unit  34  is abutted against a boss  12   i  formed on the bottom wall  12   e  and tightened with a screw  36 . As a result, the lighting circuit unit  34  can be installed on the lamp body  12 . 
     A unit cover  38  is mounted on the bottom wall  12   e  of the lamp body  12  so as to cover the lighting circuit unit  34  from below. A sealing leg portion  38 a of the unit cover  38  is inserted, through the intermediary of a sealing material  40 , into a sealing groove  12   j  (unit cover mounting sealing portion) formed in the bottom wall  12   e  of the lamp body  12  so as to surround the lighting circuit unit  34 . Concurrently, screws  42  are tightened to secure the unit cover  38  to the lamp body  12  with respect to the bosses  12   k  formed to project downward from the bottom wall  12   e  of the lamp body  12  at a plurality of positions. Such an installation of the unit cover  38  to the lamp body  12  seals the space within the unit cover  38  in which the lighting circuit unit  34  is contained from the external space of the lamp unit. A flange portion  38   b  is formed on the outer peripheral surface of the unit cover  38  so that the sealing leg portion  38   a  is not excessively inserted into the sealing groove  12   j  when installing the unit cover  38  on the lamp body  12 . 
     A portion to the rear of the lighting circuit unit  34  in the sealing groove  12   j  formed in the bottom wall  12   e  of the lamp body  12  is formed on the bottom surface of the bottom wall extension portion  12   f . A coupling rib  12   n  that extends in a longitudinal direction is formed between a portion forward of the lighting circuit unit  34  in the sealing groove  12   j  formed in the bottom wall  12   e  of the lamp body  12  and a lens sealing groove  12   b.    
     As described in detail above, in the vehicular headlamp  10  according to the present embodiment, the lighting circuit unit  34  is mounted on the outer surface of the bottom wall  12   e  of the lamp body  12 , in addition to the bulb replacement opening  12   d  being formed in the rear wall  12   c  of the lamp body  12 . The bottom wall extension portion  12   f  is formed at the rear end portion of the bottom wall  12   e , extending rearward beyond the bulb replacement opening  12   d.    
     With this structure, the following operational effects can be obtained. 
     As the rear end portion of the bottom wall  12   e  of the lamp body  12  is located adjacent the bulb replacement opening  12   d  formed in the rear wall  12   c  of the lamp body  12 , sufficient rigidity cannot be obtained with the conventional structure. However, the bottom wall extension portion  12   f  provided in the present embodiment causes the rear end portion of the bottom wall  12   e  to exhibit sufficient rigidity. As a result, the bottom wall  12   e  is protected from deflection deformation due to the weight of the lighting circuit unit  34 . This is also effective in preventing deformation of the front end opening  12   a  in the lamp body  12 , thus preventing failure in the seal between the lamp body  12  and the front lens  14 . 
     Moreover, formation of the bottom wall extension portion  12   f  on the bottom wall  12   e  of the lamp body  12  extends the area of the outer surface thereof rearward. This makes it possible, as in the present embodiment, to install the lighting circuit unit  34  on the outer surface of the bottom wall  12   e  at a position further rearward. Therefore, the lighting circuit unit  34  is installed on the bottom wall  12   e  so as to cross the rear wall  12   c  in the longitudinal direction. This suppresses deflection deformation in the bottom wall  12   e  due to the weight of the lighting circuit unit  34 . Should any deflection deformation nonetheless occur, the front end opening  12   a  is isolated from such deformation, thus protecting the seal between the lamp body  12  and the front lens  14  from failure. 
     According to the vehicular headlamp of the present embodiment in which the lighting circuit unit is installed on the outer surface of the bottom wall of the lamp body, failure of the seal between the lamp body and the front lens is effectively prevented. 
     Particularly in an oblong-shaped four-lamp system like the vehicular headlamp  10  according to the present embodiment, without the invention the bottom wall  12   e  of the lamp body  12  is susceptible to deflection deformation due to the weight of the lighting circuit unit  34 . The lens sealing groove  12   b  is also susceptible to deformation. Therefore it is particularly effective to apply the structure according to the present embodiment to such a lamp system. 
     In the present embodiment, a plurality of reinforcement ribs  12   g  are formed on, the top surface of the bottom wall extension portion  12   f , each extending rearward from the rear wall  12   c  of the lamp body  12 . This enhances the rigidity of the lamp body  12  for a portion from the rear wall  12   c  to the bottom wall extension portion  12   f . This protects the bottom wall  12   e  from deflection deformation due to the weight of the lighting circuit unit  34 . Should any deflection deformation occur, however, the front end opening  12   a  is not significantly affected by the deformation, thus effectively preventing failure of the seal between the lamp body  12  and the front lens  14 . 
     In addition, in the present embodiment, the unit cover  38  that covers the lighting circuit unit  34  is mounted on the outer surface on the bottom wall  12   e  of the lamp body  12 . The part of the unit cover mounting sealing groove  12   j  formed in the bottom wall  12   e  which is located to the rear of the lighting circuit unit  34  is formed on the bottom surface of the bottom wall extension portion  12   f . That is, such part is located at a position rearward from the rear end portion of the bottom wall  12   e . This protects the sealing groove  12   j  from deformation, which in turn contributes to maintenance of a good sealing effect between the unit cover  38  and lamp body  12 . 
     FIG. 4 is a sectional side elevational view showing a modified example of the embodiment. FIG. 5 is a perspective view in the direction of arrow V shown in FIG.  4 . 
     In the modified example, the bottom wall extension portion  12   m  is formed at a rear end portion of the bottom wall  12   e  of the lamp body  12 , extending rearward beyond the bulb replacement opening  12   d , as shown in the drawing. The bottom wall extension portion  12   m  is not formed in a plate-like shape, but is formed as a folded-back portion having a vertical cross section which is substantially U-shaped. A top surface  12   ml  of the bottom wall extension portion  12   m  is formed in an arc along the circumference of a bulb replacement opening  12   d . In the modified example, reinforcement ribs  12   g  as provided in the previously described embodiment are not required. 
     In this modified example, the provision of the bottom wall extension portion  12   m  in the form of a folded-back portion with a substantially U-shaped cross section enhances the rigidity in the bottom wall extension portion  12   m . As a result, the bottom wall  12   e  is protected from deflection deformation due to the weight of the lighting circuit unit  34 . Should some deflection deformation nevertheless occur, the front end opening  12   a  is not significantly affected by the deformation, thus preventing failure of the seal between the lamp body  12  and the front lens  14 . 
     Especially with this modified example, the top surface  12   ml  of the bottom wall extension portion  12   m  is formed in an arc-shape along the circumference of the bulb replacement opening  12   d . This further enhances the rigidity of the bottom wall extension portion  12   m.    
     Instead of forming the top surface  12   ml  of the bottom wall extension portion  12   m  in an arc-shape, the rigidity of the bottom wall extension portion  12   m  itself can be enhanced by forming it with a generally identical perpendicular cross section. In this case, formation of a plurality of reinforcement ribs  12   g  on the top surface  12   ml  of the bottom wall extension portion  12   m  as in the first embodiment enhances the rigidity of the lamp body  12  from the rear wall  12   c  to the bottom wall extension portion  12   m.    
     It should further be apparent to those skilled in the art that various changes in form and detail of the invention as shown and described above may be made. It is intended that such changes be included within the spirit and scope of the claims appended hereto.