Patent Publication Number: US-7585177-B2

Title: Discharge lamp socket

Description:
RELATED APPLICATION 
   This application claims the benefit of priority of Japanese Patent Application No. 2007-210938, filed on Aug. 13, 2007. The disclosure of that application is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present disclosure relates to a socket to which a discharge lamp for a vehicle headlight is attachable. 
   BACKGROUND 
   A known discharge lamp socket includes a starter transformer, a board on which capacitors and a spark gap are mounted, and a cover in which the starter transformer and the board are accommodated (see, e.g., Japanese Patent Document No. 2005-285368 A). The starter transformer includes a ferrite core, a secondary winding wound around the ferrite core, a sealing portion surrounding the secondary winding, and a primary winding wound around the sealing portion. A socket portion and the sealing portion are formed in a one-piece structure formed by resin molding. The socket portion includes an outer cylindrical portion inside which an outer circumferential surface of a base of the discharge lamp is fitted and an inner cylindrical portion that engage a circular recess at the bottom of the base. An inner electrode is coupled to a high-voltage end of the secondary winding, is exposed at the socket portion, and is surrounded by the outer cylindrical portion of the socket portion. Further, in order to prevent an electric discharge between the inner electrode and electronic parts, such as the capacitors and the spark gap inside the cover, the ferrite core, the secondary winding, and a coupling portion between the secondary winding and the inner electrode is sealed inside the resin molded structure. 
   However, the resin molding requires special equipment to prevent, for example, blowholes in the resin. Also, the manufacturing process is complicated. Further, in the event that a crack is generated in a rigid portion of the resin due to a temperature variation or aging degradation, an electrical insulation failure may result, making it difficult to maintain stable lighting of the lamp. Furthermore, the resin molded structure increases the weight of the socket itself, which is disadvantageous in that the optical axis of the discharge lamp is likely to deviate from proper alignment due to vibration of the vehicle. 
   SUMMARY 
   The present disclosure describes a discharge lamp socket capable of maintaining stable lighting. 
   According to an aspect of the present invention, a socket for a discharge lamp is provided. The socket includes a housing having a first housing portion and a second housing portion attachable to the first housing portion to cover the first housing portion, a starter circuit having a starter transformer and accommodated inside the housing, a central terminal coupled to the starter transformer and disposed inside the housing such that, when the discharge lamp is attached to the socket, a central electrode of the discharge lamp contacts the central terminal. The first housing portion has a base, and a first wall portion extending from the base in a direction in which the discharge lamp is attached to the socket. The second housing portion has a second wall portion which, when the second housing portion is attached to the first housing portion, overlaps with the first wall portion such that the first and second wall portions surround the central terminal on an inner side of a peripheral edge of the base. 
   Other aspects and advantages of the invention will be apparent from the following description, the drawings and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of a discharge lamp socket according to an exemplary embodiment of the present invention; 
       FIG. 2  is a side view of a first housing portion of the socket; 
       FIG. 3  is a perspective view of the socket which has been assembled; 
       FIG. 4  is a plan view illustrating a state in which a second wall portion is inserted into a groove provided on the first housing portion; 
       FIG. 5  is a enlarged sectional view illustrating a state in which the second wall portion inserted into the groove formed by first wall portions; and 
       FIG. 6  is a block diagram illustrating a starter circuit and a lighting circuit. 
   

   DETAILED DESCRIPTION 
   Various examples of embodiments of the invention will be explained below with reference to the drawings. The following exemplary embodiments do not limit the scope of the invention. 
   A socket  1  is configured to receive a discharge lamp for a headlight of a vehicle. As shown in  FIGS. 1 to 4 , the socket  1  includes a housing  2 , a starter transformer  3  and a charge-discharge circuit portion  4 . The housing  2  is a substantially a rectangular parallelepiped, the size of which is, for example, 4 cm (width)×4 cm (length)×2 cm (thickness). The starter transformer  3  and the charge-discharge circuit portion  4  form a starter circuit C 1  (see  FIG. 6 ), and are accommodated inside the housing  2 . A lighting circuit C 2 , which will be described later, is not included in the socket  1  so that the size of the socket  1  can be reduced. 
   The starter transformer  3  includes a rod-shaped magnetic core (not shown), a secondary winding  3   g  wound around the magnetic core, a resin case  3   a  covering an outer circumference of the secondary winding  3   g , and a primary winding  3   b  wound around an outer circumference of the resin case  3   a . A high-voltage side terminal  3   c  of the secondary winding  3   g  is coupled to a central terminal  7 , which is exposed from a cylindrical lamp attaching portion. The central terminal  7  is fixed to the housing  2  and contacts with the central electrode  8   a  of the discharge lamp  8  to supply a high voltage to the discharge lamp  8 . 
   The charge-discharge circuit portion  4 , which is electrically coupled to the starter transformer  3 , includes a circuit board  9  formed by insert-molding a metallic plate (not shown) with resin. The metallic plate has an electronic wiring function. The charge-discharge circuit portion  4  further includes a spark gap SG, a capacitor  10 , a resistor  11  and a coil  12 , which are mounted on the circuit board  9 . Terminals of the electronic parts SG,  10 ,  11 ,  12  are fixed onto the metallic plate by means of welding. Accordingly, as no solder is used, it is possible to prevent aging degradation of the joint portions regardless of the temperature increase caused by the discharge lamp  8 . 
   Three terminal pins (not shown) connected to the metallic plate are arranged in a connector portion  13 . The connector portion  13  and the circuit board  9  are formed in a one-piece structure. An end portion of the connector portion  13  protrudes from the housing  2 , and is connected to a plug of a connection cord (not shown) which is connected to the lighting circuit C 2 . According to such a configuration, a length of the connection cord to be connected to the connector portion  13  can be easily adjusted. Therefore, the socket  1  can be adapted to various types of vehicles. 
   The housing  2  includes a first housing portion  14  and a second housing portion  15 , both of which are made of molded resin such as PBT, PPS or LCP. That is, each of the first and second housing portion  14 ,  15  is formed in a one-piece structure. The housing  2  is assembled by fitting the second housing portion  15  onto the first housing portion  14 . The first housing portion  14  includes a base  14   a , four side walls  14   b  provided along a peripheral edge of the base  14   a  to form a cup-like shape, and a lamp attaching portion  6  formed integrally with the base  14   a . The side wall  14   b  extends from the peripheral edge of the base  14   a  in a direction in which the discharge lamp  8  is attached to the socket  1 . The lamp attaching portion  6  cylindrically extends in a direction opposite the direction in which the discharge lamp  8  is attached to the socket  1 . 
   The second housing portion  15  includes a base  15   a , and four side walls  15   b  along a peripheral edge of the base  15   a  to form a cup-like shape. When the housing  2  is assembled, each of the side walls  15   b  overlaps with a corresponding one of the side walls  14   b  of the first housing portion  14  from outer side. The side walls  14   b  of the first housing portion  14  include pawl portions  16  outwardly protruding from respective outer surfaces, and the side walls  15   b  of the second housing portion  15  are formed with rectangular engaging holes  15   c  corresponding to each of the pawl portions  16 . Thus, the housing  2  can be assembled with a one-touch operation of engaging the pawl portions  16  with the respective engaging holes  15   c.    
   The housing  2  includes a partition wall  20 , which, from the perspective of a sectional view taken along a plane substantially perpendicular to the direction in which the discharge bulb  8  is attached to the socket  1 , divides a space inside the first housing portion  14  into a first accommodating region S 1  in which the starter transformer  3  is disposed and a second accommodating region S 2  inside which the charge-discharge circuit portion  4  is disposed. The first housing portion  14  includes a first wall portion  21  which forms part of the partition wall  20  extending between the first accommodating region S 1  and the second accommodating region S 2 . The second housing portion  15  includes a second wall portion  22  which also forms part of the partition wall  20 . 
   The resin case  3   a  of the starter transformer  3  includes a first fitting portion  3   d  formed on one end thereof and a second fitting portion  3   e  formed on the other end thereof. Both the first and second fitting portions  3   d ,  3   e  are H-shaped. The first housing portion  14  includes first engaging protrusions  17  inserted into recess portions of the first fitting portion  3   d  and second engaging protrusions  18  inserted into recess portions of the second fitting portion  3   e , whereby the starter transformer  3  is fixedly attached to the first housing portion  14 . The first and second engaging protrusions  17 ,  18  are formed integrally with the first housing portion  14 . One side wall  14   b  of the first housing portion  14  is formed with a cutout portion  14   c , and likewise, the corresponding side wall  15   b  of the second housing portion  15  is formed with a cutout portion  15   d . The cutout portions  14   c ,  15   d  form a rectangular opening  19  through which the connector portion  13  is led out from inside the housing so as to be exposed to the outside. 
   According to the configuration described above, the socket  1  may consist of four components, namely, the starter transformer  3 , the charge-discharge circuit portion  4 , the first housing portion  14  and the second housing portion  15 . Accordingly, when assembling the socket  1 , it is sufficient for only the starter transformer  3  and the charge-discharge circuit portion  4  to be placed in the first and the second accommodating regions S 1 , S 2  respectively. Therefore, the assembly can be improved. 
   The partition wall  20 , which is arranged to surround the central terminal  7 , is now described in detail. The partition wall  20  includes the first wall portion  21  extending from the base  14   a  of the first housing portion  14  and the second wall portion  22  extending from the base  15   a  of the second housing portion  15  such that, when the second housing portion  15  is attached to the first housing portion  14 , the second wall portion  22  overlaps with the first wall portion  21  in a direction perpendicular to the direction in which the discharge lamp  8  is attached to the socket. 
   The first wall portion  21  includes a first wall section  21   a  extending in a C-shape so as to surround the central terminal  7 , a second wall section  21   b  extending in a larger C-shape so as to surround the first wall section  21   a , a third wall section  21   c  extending in a U-shape from one end of the second wall section  21   b  toward the side wall  14   b  and along the side wall  14   b  so as to surround a end portion  3   f  of the starter transformer  3  on a high-voltage side; a fourth wall section  21   d  extending in a larger U-shape so as to surround the third wall section  21   c , a fifth wall section  21   e  extending in an L-shape from an end of the first wall section  21   a  so as to surround a high-voltage side terminal  3   c  of the starter transformer  3 , and a sixth wall section  21   f  extending in a larger L-shape from the other end of the second wall section  21   b  so as to surround the fifth wall section  21   e.    
   The first wall section  21   a  and the second wall section  21   b  are arranged to extend substantially in parallel one another. The third wall section  21   c  and the fourth wall section  21   d  are arranged to extend substantially in parallel to one another. The fifth wall section  21   e  and the sixth wall section  21   f  are arranged to extend substantially in parallel one another. A first substantially C-shaped groove  23   a  is formed between the first wall and second wall sections  21   a ,  21   b . A second substantially U-shaped groove  23   b  is formed between the third and fourth wall sections  21   c ,  21   d . A third substantially L-shaped groove  23   c  is formed between the fifth and sixth wall sections  21   e ,  21   f  The first and third grooves  23   a ,  23   c  can communicate with one another. The second groove  23   b  is opened at one end the fourth wall section  21   d  which is separated from the second wall section  21   b.    
   On the other hand, the second wall portion  22  is arranged to correspond to the first wall portion  21 . More specifically, the second wall portion  22  includes a first C-shaped section  22   a  to be inserted into the first groove  23   a , a second U-shaped section  22   b  to be inserted into the second groove  23   b , and a third L-shaped section  22   c  to be inserted into the third groove  23   c . The second wall portion  22  further includes a fourth C-shaped section  22   d  extending from an one end of the second section  22   b  adjacently along an outer surface of the second wall section  21   b . The second wall portion  22  further includes a rod-shaped protruding portion  15   e  extending inside the first section  22   a . When the second housing portion  15  is attached to the first housing portion  14 , this protruding portion  15   e  is inserted into a through-hole portion  14   d  formed on an inner side of the first wall section  21   a . The central terminal  7  is also inserted into this through-hole portion  14   d  and is fixed by the protruding portion  15   e.    
   According to the partition wall  20  described above, a high voltage electric discharge is prevented from being generated between the high-voltage side terminal  3   c  of the secondary wiring of the starter transformer  3  and exposed terminal portions of the spark gap SG, the capacitor  10 , the resistor  11  and the coil  12  that are mounted on the circuit board  9 . Further, a high voltage electric discharge between the central terminal  7  and the exposed terminal portions of the charge-discharge circuit portion  4  also is prevented by the partition wall  20 . According to the exemplary embodiment described above, the partition wall  20  is formed inside the housing  2  only by attaching the second housing portion  15  to the first housing portion  14  such that the first wall portion  21  and the second wall portion  22  overlap one another. Accordingly, a reliable voltage-resistance structure can be created by partition wall  20  without the need for resin molding, i.e. without increasing the weight of the socket. In addition, because the partition wall  20  has a combined structure of overlapping first and second wall portions  21 ,  22 , an even more stable lighting performance can be maintained. 
   As shown in  FIG. 5 , when the second wall portion  22  is inserted into the grooves  23   a  to  23   c  formed by the first wall portion  21 , the first wall portion  21  and the second wall portion  22  overlap one another with a gap G being formed between the wall portions. This U-shaped gap G increases the length of a creeping passage along the partition wall  20 , thereby preventing an electric discharge leakage from the partition wall  20 . Thus, it is possible to provide a simple and effective electric insulating wall. For example, where the starter voltage to be generated at the central terminal  7  reaches 22 kV, it is preferable that the length of the gap G be 22 mm or more. However, the first wall portion  21  and the second wall portion  22  may tightly overlap with each other without any gap between. 
   Although a sufficient electric discharge insulation can be obtained with the partition wall  20  described above, thermosetting resin may be filled in the first accommodating region S 1  with the starter transformer  3  being attached to the first accommodating region S 1 . According to such a configuration, a corona discharge from the starter transformer  3  can be prevented from being generated, and it becomes possible to generate high-voltage pulses more effectively. Moreover, the starter transformer  3  can be prevented from being adversely affected by moisture or humidity entering the socket  1 . 
   Thermosetting resin also may be inserted from a circular resin charging port (not shown), which may be formed on the base  14   a  of the first housing portion  14  to communicate with the second accommodating region S 2 . According to such a configuration, the charge-discharge circuit portion  4  is prevented from being adversely affected by the moisture or humidity entering the socket  1 . An example of the thermosetting resin to be provided in the first and/or second accommodating region S 1 , S 2  to resin-seal the starter transformer  3  and/or the charge-discharge circuit portion  4  is silicon resin, which changes from liquid to gel when it is heated at about 100° C. The thermosetting resin also may be urethane resin or epoxy resin. Thermosetting resin may be such a resin that it is cured after being inserted into the housing  2  with any special treatments. 
   Next, the starter circuit C 1  and the lighting circuit C 2 , which is a separate component to be connected to the connection cord having the plug to be coupled to the connector portion  13 , will be briefly explained below. 
   As shown in  FIG. 6 , in the lighting circuit C 2 , 12V electricity supplied from a battery mounted on a vehicle is provided to an input filter through which various electric noises are removed, and then, the voltage is boosted up from 12V to a certain voltage (for example, to 45V in a steady state, and to 400V just before lighting) through a DC-DC converter  32 . The boosted DC voltage is converted to AC voltage through a full bridge circuit  33  and is supplied to the starter circuit C 1 . When turning on the discharge lamp  8 , a voltage boosted by a booster circuit  34  is supplied to the starter circuit C 1 . Electric power inside the lighting circuit C 2  is controlled by a control circuit portion  35 . 
   In the starter circuit C 1 , electric charges are stored in the capacitor  10  by the output voltage sent from the booster circuit  34 . When the voltage between terminals of the capacitor  10  exceeds a electrical breakdown threshold value of the spark gap SG breaks, the spark gap SG is turned on, and an instantaneous electric current flows in the primary winding  3   b  of the starter transformer  3 , whereby a high voltage pulse (the starter voltage 22 kV) is induced between the terminals of the secondary winding  3   g , that is, at the high-voltage side terminal  3   c  of the secondary winding  3   g . This high-voltage pulse is superimposed on an output voltage, which is sent from the full bridge circuit  33  through a filter composed of the coil  12  and the capacitor  41 , and is supplied to the discharge lamp  8 . This high-voltage pulse causes an electrical breakdown in the discharge lamp  8 , whereby the discharge lamp  8  starts lighting. 
   When the discharge lamp  8  starts lighting, impedance is lowered. Thus, the output voltage of DC-DC converter circuit  32  is lowered so that the voltage between the terminals of the capacitor  10  becomes less than the electrical breakdown threshold value of the spark gap SG. Accordingly, a high-voltage pulse is not induced at the high-voltage side terminal  3   c  of the secondary winding  3   g  in the starter transformer  3 . In the manner described above, at the time of lighting the discharge lamp  8 , the high-voltage pulse is induced at the high-voltage side terminal  3   c  of the secondary winding  3   d  in the starter transformer  3 . 
   The resistor  11  is provided for the purpose of discharging the electric charges stored in the capacitor  10  when a switch connected in series to the battery is turned off. 
   Although the foregoing description has been made in connection with a particular embodiment of the present invention, those skilled in the art will understand that various changes and modification may be made therein without departing from the present invention. 
   For example, the housing  2  may be covered by a metallic cap (not shown) such that the resin charging port (not shown) on the base  14   a  of the first housing portion  14  can be closed. Such a metallic cap is effective for reducing a generation of electromagnetic emission noise. 
   Further, in order to form multiple parallel grooves, the first wall portion may include three or more parallel wall sections and the second wall portion may include two or more parallel wall sections to be inserted into each of the grooves. According to such a configuration, a meandering gap is formed so that the creeping passage along the partition wall can be extended more. Furthermore, the first housing portion  14  may be formed in a one-piece structure. For example, the first wall portion  21  and a bottom wall portion of the first wall portion  21  may be formed as a separate structure from the side walls  14   b.    
   Moreover, instead of providing the connector portion  13 , one end of a connection cord may be directly coupled to the circuit board  9 . In such a case, the connection cord may be led out from the socket  1 , and the other end of the connection cord may have a socket to be connected to a connector portion of the lighting circuit C 2 . 
   Other implementations are within the scope of the claims.