Abstract:
A vehicular headlamp comprising a lighting compartment, first and second reflectors, a bulb, and a lighting circuit unit. The lighting compartment is defined by a lamp body and a front lens. The first and second reflectors are provided in the lighting compartment, and the second reflector is beside the first reflector. The bulb is mounted on the second reflector. The lighting circuit unit is provided below the first reflector and electrically connected to the bulb.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a four-lamp vehicular headlamp system, more particularly to a vehicular headlamp having a discharge bulb mounted on a sub-beam reflector. 
     2. Description of the Related Art 
     Discharge bulbs can provide high-luminance illumination and are increasingly used as a light source for vehicular headlamps. Four-lamp vehicular headlamp systems can provide enhanced vision under illumination with sub-beams if the sub-beam reflectors are each fitted with a discharge bulb. 
     If a vehicular headlamp is fitted with a discharge bulb, a lighting circuit unit must be provided to light the discharge bulb by applying high voltage to it. In the conventional vehicular headlamp, the lighting circuit unit is provided below the reflector on which the discharge bulb is mounted. This means if the discharge bulb is mounted on a sub-beam reflector, the lighting circuit unit is provided below the sub-beam reflector. 
     FIG. 5 shows a half section of a conventional four-lamp vehicular headlamp system comprising a lighting compartment  106  formed of a lamp body  102  and a front lens  104 , a main beam reflector  108 M and a sub-beam reflector  108 S placed side by side in the lighting compartment  106 , and a discharge bulb  110  mounted on the sub-beam reflector  108 S. If a lighting circuit unit  112  is provided below the sub-beam reflector  108 S, the following problem occurs. 
     With the four-lamp headlamp system, the main beam or high beam is not lit when the illumination with the sub-beam or low beam is on and the space around the sub-beam reflector  108 S in the lighting compartment  106  becomes hot by the heat generation from the discharge bulb  110  and the lighting circuit unit  112  while the space around the main beam reflector  108 M remains cold. As a result, haze is most likely to occur on the inner surface of that portion of the front lens  104  which is in front of the main beam reflector  108 M. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under these circumstances and has as an object providing a four-lamp vehicular headlamp system that has a discharge bulb mounted on each of the sub-beam reflectors and which yet is effectively protected against haze formation on the inner faces of the front lenses. 
     The present invention aims to attain the stated object by choosing a specific position for installing the lighting circuit unit. 
     That is, the present invention provides a vehicular headlamp comprising a lighting compartment formed of a lamp body and a front lens, a main beam reflector and a sub-beam reflector placed side by side in the lighting compartment, and a discharge bulb mounted on said sub-beam reflector, wherein a lighting circuit unit for lighting said discharge bulb is provided below said main beam reflector. 
     By the expression “provided below the main beam reflector” is meant that the position of the horizontal center of the lighting circuit unit does not coincide with the middle point between the optical axes of the main beam reflector and the sub-beam reflector but is offset toward the optical axis of the main beam reflector. As long as this condition is met and the lighting circuit unit is “below the main beam reflector”, it may be provided either within or outside the lighting compartment. 
     As stated above, the vehicular headlamp of the present invention comprises a lighting compartment formed of a lamp body and a front lens, a main beam reflector and a sub-beam reflector placed side by side in the lighting compartment; although a discharge bulb is mounted on the sub-beam reflector, a lighting circuit unit for lighting the discharge bulb is provided below the main beam reflector, so under illumination with the sub-beam, the space around the sub-beam reflector in the lighting compartment becomes hot by the heat generation from the discharge bulb and the space around the main beam reflector also becomes hot by the heat generation from the lighting circuit unit. As a result, the temperature in the lighting compartment can be maintained generally uniform to ensure effective prevention of haze formation on the inner surface of the front lens. 
     The conventional vehicular headlamp has another problem peculiar to cold climates. During illumination with the sub-beam, snow deposited on that part of the front lens which is in front of the main beam reflector does not readily melt, so that when the sub-beam is turned off and the main beam comes on, the light reflected from the main beam reflector is not sufficiently projected ahead of the front lens that it becomes difficult to secure the intended luminous intensity distribution. In contrast, the design of the present invention permits the temperature in every part of the lighting compartment to rise during illumination with the sub-beam so that the entire surface of the front lens has a snow melting capability. As a result, when the sub-beam is switched to the main beam, the latter can provide an adequate luminous intensity distribution. 
     Preferably, the vehicular headlamp according to the present invention includes a passageway through which the heat generated from the lighting circuit unit is directed toward the front of the main beam reflector is formed in the lighting compartment. With this design, the efficiency with which that part of the front lens which is in front of the main beam reflector becomes hot during illumination with the sub-beam is sufficiently enhanced to produce a greater effect in preventing haze formation on the inner surface of the front lens and melting the snow deposited on that front lens. 
     The specific design of the “passageway” is not limited in any particular way. For example, if an extension reflector is provided in front of said both reflectors in said lighting compartment, the passageway can be provided by forming a cutout at the lower end of said extension reflector in front of the main beam reflector. By this design, the heat generated from the lighting circuit unit can be effectively directed to a site in front of the main beam reflector. 
     During illumination with the sub-beam, the corners at the lower end of the space around the main beam reflector in the lighting compartment tend to become colder than other areas to have a greater chance of haze formation. To deal with this problem, preferably, an air hole penetrating the lamp body is formed near its bottom at the end of the side where the main beam reflector is provided. With this design, atmospheric air is introduced into the lighting compartment via said air hole to provide an even greater anti-haze effect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a vehicular headlamp according to an embodiment of the present invention; 
     FIG. 2 is a section view taken along the line II—II of FIG. 1; 
     FIG. 3 is a section view taken along the line III—III of FIG. 1; 
     FIG. 4 is a section view taken along the line IV—IV of FIG. 1; and 
     FIG. 5 is a front view of a conventional vehicular headlamp. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention is described below with reference to accompanying drawings. 
     FIG. 1 is a front view of a vehicular headlamp according to an embodiment of the invention; FIGS. 2-4 are sections II—II, III—III and IV—IV, respectively, of FIG.  1 . 
     As these figures show, the vehicular headlamp according to the embodiment which is generally indicated by  10  is a four-lamp headlamp system and comprises a lighting compartment  16  formed of a lamp body  12  and a front lens  14 , and a main beam reflector  18 M and a sub-beam reflector  18 S are placed side by side in the lighting compartment  16 . The two reflectors  18 M and  18 S are supported on the lamp body  12  in such a way that they can change directions either up and down or from right to left. An extension reflector  20  is provided in front of the reflectors  18 M and  18 S in the lighting compartment  16 . 
     The front lens  14  is constituted by a transparent lens, and the luminous intensity distribution is controlled by the reflectors  18 M and  18 S. 
     Namely, the main beam reflector  18 M has a reflective face  18 M a  formed of a plurality of reflector elements  18 M s  and a halogen bulb  22  is mounted on the optical axis Ax 1 . The light from the halogen bulb  22  is diffusely deflected and reflected by the reflective face  18 M a  to generate illumination for the main beam. 
     For the same purpose, the sub-beam reflector  18 S has a reflective face  18 S a  formed of a plurality of reflector elements  18 S s  and a discharge bulb (metal halide bulb)  24  is mounted on the optical axis Ax 2 , with a shade  26  being provided to cover the area in front of the discharge bulb  18 . The light from the discharge bulb  24  is diffusely deflected and reflected by the reflective face  18 S a  to generate illumination for the sub-beam. 
     The vehicular headlamp  10  according to the embodiment forms a luminous intensity distribution pattern for the sub-beam only by the sub-beam illumination generated by lighting of the discharge bulb  24  whereas a luminous intensity distribution pattern for the main beam is formed by the combination of the sub-beam illumination and the main beam illumination created by simultaneous lighting of the discharge bulb  24  and the halogen bulb  22 . 
     The discharge bulb  22  needs high voltage to be lit and, hence, it is connected to a lighting circuit unit  32  via a bulb socket  28  and a high-voltage cord  30 . The lighting circuit unit  32  comprises a starter circuit and a stabilizer circuit placed within a or outside which, in turn, is placed within a unit holder  12   b  formed under the bottom wall  12   a  of the lamp body  12  and below the main beam reflector  18 M. The horizontal center of the lighting circuit unit  12   b  does not coincide with the optical axis Ax 1  of the main beam reflector  18 M but is slightly offset toward the optical axis Ax 2  of the sub-beam reflector  18 S. 
     An opening  12   c  is formed at the back of the unit holder  12   b  and fitted with a cover  34  to close it. The unit holder  12   b  and the cover  34  have ribs  12   d ,  12   e ,  12   f ,  34   a  and  34   b  for retaining the lighting circuit unit  32 . A hole  12   g  through which to pass the high-voltage cord  30  is formed in the rear part of the bottom wall  12   a  of the lamp body  12 . 
     The extension reflector  20  comprises a front panel portion  20 A formed along the inner surface  14   a  of the front lens  14 , a peripheral flange portion  20 B formed along the periphery of the front panel portion  20 A, and a pair of tubular portions  20 C and  20 D formed side by side in front of the reflectors  18 M and  18 S, respectively. The tubular portions  20 C and  20 D slightly taper toward the back and their rear end rims  20 C a  and  20 D a  are formed in generally the same shape as the front end openings  18 M b  and  18 S b  of the reflectors  18 M and  18 S. The extension reflector  20  has a cutout  20   a  formed at its lower end in front of the main beam reflector  18 M. The cutout  20   a  extends from the front panel portion  20 A to the peripheral flange portion  20 B. 
     The lamp body  12  has three air holes  12   h ,  12   i  and  12   j  that penetrate it from back to front; the holes  12   h  and  12   i  are formed near the bottom of the lamp body  12  at horizontal opposite ends whereas the hole  12   j  is formed near the top at its horizontal center. These air holes  12   h ,  12   i  and  12   j  are each fitted with a rubber tube  36  so that they are open downward. A guard rib  12   k  is formed over each of those air holes  12   h ,  12   i  and  12   j  in the lamp body  12 . 
     As described above in detail, the vehicular headlamp of the invention  10  comprises the lighting compartment  16  formed of the lamp body  12  and the f front lens  14 , the main beam ref lector  18 M and the sub-beam ref lector  18 S placed side by side in the lighting compartment  16 ; although the discharge bulb  24  is mounted on the sub-beam ref lector  18 S, the lighting circuit unit  32  for lighting the discharge bulb  24  is provided below the main beam reflector  18 M, so under illumination with the sub-beam, the space around the sub-beam reflector  18 S in the lighting compartment  16  becomes hot by the heat generation from the discharge bulb  24  and the space around the main beam reflector  18 M also becomes hot by the heat generation from the lighting circuit unit  32 . As a result, the temperature in the lighting compartment  16  can be maintained generally uniform to ensure effective prevention of haze formation on the inner surface  14   a  of the front lens  14 . 
     Particularly in the case of the present embodiment where the front lens  14  is constituted by a transparent lens, haze on its inner surface  14   a  will deteriorate the appearance of the lighting device even if the luminous intensity distribution that it produces is in no way affected. This problem can most effectively be prevented by adopting the design of the embodiment. 
     What is more, the design of the embodiment permits the temperature in every part of the lighting compartment  16  to rise during illumination with the sub-beam so that the entire surface of the front lens  14  has a snow melting capability. As a result, when the sub-beam is switched to the main beam, the latter can provide an adequate luminous intensity distribution even if the headlamp is used in cold climates. 
     The vehicular headlamp  10  according to the embodiment described above has the extension reflector  20  provided in front of the reflectors  18 M and  18 S in the lighting compartment  16 . Since the extension reflector  20  has the cutout  20   a  formed at its lower end in front of the main beam reflector  18 M, a passageway through which the heat generated from the lighting circuit unit  32  is directed toward the front of the main beam reflector  18 M can be formed in the lighting compartment  16 . With this design, the efficiency with which that part of the front lens  14  which is in front of the main beam reflector  18 M becomes hot during illumination with the sub-beam is sufficiently enhanced to produce a greater effect in preventing haze formation on the inner surface  14   a  of the front lens  14  and melting the snow deposited on said front lens. 
     The vehicular headlamp  10  according to the embodiment described above also has the air hole  12   h  penetrating the lamp body  12  formed near its bottom at the end of the side where the main beam reflector  18 M is provided. With this design, atmospheric air can be introduced into the lighting compartment  16  via the air hole  12   h  to provide an even greater anti-haze effect. During illumination with the sub-beam, the corners at the lower end of the space around the main beam reflector  18 M in the lighting compartment  16  tend to become colder than other areas and have a greater chance of haze formation. This problem can most effectively be prevented by forming the air hole  12   h . In the embodiment described above, the lamp body  12  also has the air hole  12   j  formed near the top at its horizontal center and convection can easily be created in the space around the main beam reflector  18 M in the lighting compartment  16 , providing an even greater anti-haze effect. 
     While only a certain embodiment of the invention has been specifically described herein, it will be apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention. 
     The present invention is based on Japanese Patent Application No. Hei. 11-63732 which is incorporated herein by reference.