Discharge lamp socket

A 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 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 first and second housing portions are attached together, 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.

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.

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 socket1is configured to receive a discharge lamp for a headlight of a vehicle. As shown inFIGS. 1 to 4, the socket1includes a housing2, a starter transformer3and a charge-discharge circuit portion4. The housing2is a substantially a rectangular parallelepiped, the size of which is, for example, 4 cm (width)×4 cm (length)×2 cm (thickness). The starter transformer3and the charge-discharge circuit portion4form a starter circuit C1(seeFIG. 6), and are accommodated inside the housing2. A lighting circuit C2, which will be described later, is not included in the socket1so that the size of the socket1can be reduced.

The starter transformer3includes a rod-shaped magnetic core (not shown), a secondary winding3gwound around the magnetic core, a resin case3acovering an outer circumference of the secondary winding3g, and a primary winding3bwound around an outer circumference of the resin case3a. A high-voltage side terminal3cof the secondary winding3gis coupled to a central terminal7, which is exposed from a cylindrical lamp attaching portion. The central terminal7is fixed to the housing2and contacts with the central electrode8aof the discharge lamp8to supply a high voltage to the discharge lamp8.

The charge-discharge circuit portion4, which is electrically coupled to the starter transformer3, includes a circuit board9formed by insert-molding a metallic plate (not shown) with resin. The metallic plate has an electronic wiring function. The charge-discharge circuit portion4further includes a spark gap SG, a capacitor10, a resistor11and a coil12, which are mounted on the circuit board9. Terminals of the electronic parts SG,10,11,12are 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 lamp8.

Three terminal pins (not shown) connected to the metallic plate are arranged in a connector portion13. The connector portion13and the circuit board9are formed in a one-piece structure. An end portion of the connector portion13protrudes from the housing2, and is connected to a plug of a connection cord (not shown) which is connected to the lighting circuit C2. According to such a configuration, a length of the connection cord to be connected to the connector portion13can be easily adjusted. Therefore, the socket1can be adapted to various types of vehicles.

The housing2includes a first housing portion14and a second housing portion15, both of which are made of molded resin such as PBT, PPS or LCP. That is, each of the first and second housing portion14,15is formed in a one-piece structure. The housing2is assembled by fitting the second housing portion15onto the first housing portion14. The first housing portion14includes a base14a, four side walls14bprovided along a peripheral edge of the base14ato form a cup-like shape, and a lamp attaching portion6formed integrally with the base14a. The side wall14bextends from the peripheral edge of the base14ain a direction in which the discharge lamp8is attached to the socket1. The lamp attaching portion6cylindrically extends in a direction opposite the direction in which the discharge lamp8is attached to the socket1.

The second housing portion15includes a base15a, and four side walls15balong a peripheral edge of the base15ato form a cup-like shape. When the housing2is assembled, each of the side walls15boverlaps with a corresponding one of the side walls14bof the first housing portion14from outer side. The side walls14bof the first housing portion14include pawl portions16outwardly protruding from respective outer surfaces, and the side walls15bof the second housing portion15are formed with rectangular engaging holes15ccorresponding to each of the pawl portions16. Thus, the housing2can be assembled with a one-touch operation of engaging the pawl portions16with the respective engaging holes15c.

The housing2includes a partition wall20, which, from the perspective of a sectional view taken along a plane substantially perpendicular to the direction in which the discharge bulb8is attached to the socket1, divides a space inside the first housing portion14into a first accommodating region S1in which the starter transformer3is disposed and a second accommodating region S2inside which the charge-discharge circuit portion4is disposed. The first housing portion14includes a first wall portion21which forms part of the partition wall20extending between the first accommodating region S1and the second accommodating region S2. The second housing portion15includes a second wall portion22which also forms part of the partition wall20.

The resin case3aof the starter transformer3includes a first fitting portion3dformed on one end thereof and a second fitting portion3eformed on the other end thereof. Both the first and second fitting portions3d,3eare H-shaped. The first housing portion14includes first engaging protrusions17inserted into recess portions of the first fitting portion3dand second engaging protrusions18inserted into recess portions of the second fitting portion3e, whereby the starter transformer3is fixedly attached to the first housing portion14. The first and second engaging protrusions17,18are formed integrally with the first housing portion14. One side wall14bof the first housing portion14is formed with a cutout portion14c, and likewise, the corresponding side wall15bof the second housing portion15is formed with a cutout portion15d. The cutout portions14c,15dform a rectangular opening19through which the connector portion13is led out from inside the housing so as to be exposed to the outside.

According to the configuration described above, the socket1may consist of four components, namely, the starter transformer3, the charge-discharge circuit portion4, the first housing portion14and the second housing portion15. Accordingly, when assembling the socket1, it is sufficient for only the starter transformer3and the charge-discharge circuit portion4to be placed in the first and the second accommodating regions S1, S2respectively. Therefore, the assembly can be improved.

The partition wall20, which is arranged to surround the central terminal7, is now described in detail. The partition wall20includes the first wall portion21extending from the base14aof the first housing portion14and the second wall portion22extending from the base15aof the second housing portion15such that, when the second housing portion15is attached to the first housing portion14, the second wall portion22overlaps with the first wall portion21in a direction perpendicular to the direction in which the discharge lamp8is attached to the socket.

The first wall portion21includes a first wall section21aextending in a C-shape so as to surround the central terminal7, a second wall section21bextending in a larger C-shape so as to surround the first wall section21a, a third wall section21cextending in a U-shape from one end of the second wall section21btoward the side wall14band along the side wall14bso as to surround a end portion3fof the starter transformer3on a high-voltage side; a fourth wall section21dextending in a larger U-shape so as to surround the third wall section21c, a fifth wall section21eextending in an L-shape from an end of the first wall section21aso as to surround a high-voltage side terminal3cof the starter transformer3, and a sixth wall section21fextending in a larger L-shape from the other end of the second wall section21bso as to surround the fifth wall section21e.

The first wall section21aand the second wall section21bare arranged to extend substantially in parallel one another. The third wall section21cand the fourth wall section21dare arranged to extend substantially in parallel to one another. The fifth wall section21eand the sixth wall section21fare arranged to extend substantially in parallel one another. A first substantially C-shaped groove23ais formed between the first wall and second wall sections21a,21b. A second substantially U-shaped groove23bis formed between the third and fourth wall sections21c,21d. A third substantially L-shaped groove23cis formed between the fifth and sixth wall sections21e,21fThe first and third grooves23a,23ccan communicate with one another. The second groove23bis opened at one end the fourth wall section21dwhich is separated from the second wall section21b.

On the other hand, the second wall portion22is arranged to correspond to the first wall portion21. More specifically, the second wall portion22includes a first C-shaped section22ato be inserted into the first groove23a, a second U-shaped section22bto be inserted into the second groove23b, and a third L-shaped section22cto be inserted into the third groove23c. The second wall portion22further includes a fourth C-shaped section22dextending from an one end of the second section22badjacently along an outer surface of the second wall section21b. The second wall portion22further includes a rod-shaped protruding portion15eextending inside the first section22a. When the second housing portion15is attached to the first housing portion14, this protruding portion15eis inserted into a through-hole portion14dformed on an inner side of the first wall section21a. The central terminal7is also inserted into this through-hole portion14dand is fixed by the protruding portion15e.

According to the partition wall20described above, a high voltage electric discharge is prevented from being generated between the high-voltage side terminal3cof the secondary wiring of the starter transformer3and exposed terminal portions of the spark gap SG, the capacitor10, the resistor11and the coil12that are mounted on the circuit board9. Further, a high voltage electric discharge between the central terminal7and the exposed terminal portions of the charge-discharge circuit portion4also is prevented by the partition wall20. According to the exemplary embodiment described above, the partition wall20is formed inside the housing2only by attaching the second housing portion15to the first housing portion14such that the first wall portion21and the second wall portion22overlap one another. Accordingly, a reliable voltage-resistance structure can be created by partition wall20without the need for resin molding, i.e. without increasing the weight of the socket. In addition, because the partition wall20has a combined structure of overlapping first and second wall portions21,22, an even more stable lighting performance can be maintained.

As shown inFIG. 5, when the second wall portion22is inserted into the grooves23ato23cformed by the first wall portion21, the first wall portion21and the second wall portion22overlap 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 wall20, thereby preventing an electric discharge leakage from the partition wall20. 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 terminal7reaches 22 kV, it is preferable that the length of the gap G be 22 mm or more. However, the first wall portion21and the second wall portion22may tightly overlap with each other without any gap between.

Although a sufficient electric discharge insulation can be obtained with the partition wall20described above, thermosetting resin may be filled in the first accommodating region S1with the starter transformer3being attached to the first accommodating region S1. According to such a configuration, a corona discharge from the starter transformer3can be prevented from being generated, and it becomes possible to generate high-voltage pulses more effectively. Moreover, the starter transformer3can be prevented from being adversely affected by moisture or humidity entering the socket1.

Thermosetting resin also may be inserted from a circular resin charging port (not shown), which may be formed on the base14aof the first housing portion14to communicate with the second accommodating region S2. According to such a configuration, the charge-discharge circuit portion4is prevented from being adversely affected by the moisture or humidity entering the socket1. An example of the thermosetting resin to be provided in the first and/or second accommodating region S1, S2to resin-seal the starter transformer3and/or the charge-discharge circuit portion4is 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 housing2with any special treatments.

Next, the starter circuit C1and the lighting circuit C2, which is a separate component to be connected to the connection cord having the plug to be coupled to the connector portion13, will be briefly explained below.

As shown inFIG. 6, in the lighting circuit C2, 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 converter32. The boosted DC voltage is converted to AC voltage through a full bridge circuit33and is supplied to the starter circuit C1. When turning on the discharge lamp8, a voltage boosted by a booster circuit34is supplied to the starter circuit C1. Electric power inside the lighting circuit C2is controlled by a control circuit portion35.

In the starter circuit C1, electric charges are stored in the capacitor10by the output voltage sent from the booster circuit34. When the voltage between terminals of the capacitor10exceeds 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 winding3bof the starter transformer3, whereby a high voltage pulse (the starter voltage 22 kV) is induced between the terminals of the secondary winding3g, that is, at the high-voltage side terminal3cof the secondary winding3g. This high-voltage pulse is superimposed on an output voltage, which is sent from the full bridge circuit33through a filter composed of the coil12and the capacitor41, and is supplied to the discharge lamp8. This high-voltage pulse causes an electrical breakdown in the discharge lamp8, whereby the discharge lamp8starts lighting.

When the discharge lamp8starts lighting, impedance is lowered. Thus, the output voltage of DC-DC converter circuit32is lowered so that the voltage between the terminals of the capacitor10becomes 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 terminal3cof the secondary winding3gin the starter transformer3. In the manner described above, at the time of lighting the discharge lamp8, the high-voltage pulse is induced at the high-voltage side terminal3cof the secondary winding3din the starter transformer3.

The resistor11is provided for the purpose of discharging the electric charges stored in the capacitor10when 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 housing2may be covered by a metallic cap (not shown) such that the resin charging port (not shown) on the base14aof the first housing portion14can 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 portion14may be formed in a one-piece structure. For example, the first wall portion21and a bottom wall portion of the first wall portion21may be formed as a separate structure from the side walls14b.

Moreover, instead of providing the connector portion13, one end of a connection cord may be directly coupled to the circuit board9. In such a case, the connection cord may be led out from the socket1, and the other end of the connection cord may have a socket to be connected to a connector portion of the lighting circuit C2.

Other implementations are within the scope of the claims.