Patent Publication Number: US-9414473-B2

Title: Discharge lamp with contact paths within the base

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
     This application is the U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/IB2013/052819, filed on Apr. 9, 2013, which claims the benefit of U.S. Provisional Patent Application No. 61/638,553, filed on Apr. 26, 2012. This application is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lamp and a method of manufacturing a lamp, in particular to a discharge lamp, and more specifically to a lamp for use in a vehicle headlight. 
     BACKGROUND OF THE INVENTION 
     Electrical discharge lamps, in particular high intensity discharge (HID) lamps are widely used today, e. g. in vehicle headlights. While first generations of such automotive HID lamps comprised a lamp base only for mechanical mounting and electrical contacting of a burner, currently developed lamps include circuitry for operation and/or ignition of the burner integrated within the lamp base. 
     The present invention deals with providing electrical contacts within the lamp base to components of an operating circuit. 
     U.S. 2006/0119282 A1 describes a high-pressure discharge lamp having a lamp base with an integrated starting apparatus. An electromagnetic shield is provided, which is connected to the ground reference potential of an operating device. The electromagnetic shield is provided as a metal housing which surrounds the lamp base, and has an aperture for a discharge vessel and for electrical connection of the lamp. The metal housing is made from aluminum or from an aluminum/magnesium alloy, or from a galvanized steel sheet. Inside, a lead frame is provided with electrical components of the starting apparatus, which comprises metallic webs embedded in electrically insulating plastic. A metallic tongue protrudes from the lead frame and out of the interior of the lamp base. In the mounted state, the metallic tongue of the metal web is in electrical and mechanical contact with a wall part of the metal housing. The metallic web, in a similar manner to a leaf spring, bears against the metal housing with a clamping fit. 
     SUMMARY OF THE INVENTION 
     It may be considered an object to provide a lamp and a manufacturing method therefor allowing reliable electrical contacting. 
     This object is solved by a lamp and by a method for manufacturing a lamp as described and claimed herein. Dependent claims refer to preferred embodiments of the invention. 
     The lamp according to the invention comprises a burner, preferably a HID (high intensity discharge) burner, fixed to a lamp base. An operating circuit is provided within the base. The operating circuit serves to supply electrical power to the burner and may comprise circuitry for ignition and/or for supplying an alternating current to the lamp during steady state operation. Preferably, the operating circuit comprises both an ignitor and a driver circuit, such that the lamp may be fully operated by a mere supply of vehicle onboard voltage. 
     According to the invention, at least one elongate contact path element is provided extending within the base. The contact path element is preferably a metal strip or web, e.g. made of sheet metal, such as steel. The contact path element is electrically connected to at least one component of the operating circuit, preferably to a circuit carrier, such as a printed circuit board, mounting a plurality of electrical components of the operating circuit. 
     The invention provides that the contact path element is supported within the base, preferably within a base housing, in a special way. A first portion of the contact path element is fixed within the base, and a second portion thereof is slidably received within the base. Thus, the first portion of the contact path element is fixed and not moveable relative to the base, whereas the second portion is only slidably received and not fully fixed, such that it may move in longitudinal direction thereof. 
     Further, the contact path element is fixed to the operating circuit at a position arranged in longitudinal direction from the second portion thereof. 
     As will be explained below with reference to preferred embodiments, this special support of the contact path element has been found advantageous for simple manufacture and reliable electrical contact. The contact path element retains, during manufacture, a certain flexibility to longitudinally move while being slidably received within the base. This allows to establish a reliable connection, e.g. by soldering, welding or other types of connection fixing the contact path element to the operating circuit. A certain amount of slidable movement of the second portion of the contact path element allows compensating for possible manufacturing tolerances to ascertain that reliable contact is made. 
     In the manufacturing method according to the invention, a lamp base as described is provided, to which a burner may already be fixed, or where a burner may later be fit. During manufacture, the contact path element is fixed to the operating circuit at a position, which is arranged in longitudinal direction of the second portion. 
     According to preferred embodiments of the invention, the base comprises a non-conductive holder element, preferably made of plastic, which may be arranged within, or may be part of a housing of the base. The contact path element may be fixed at the first portion thereof to the holder element, e.g. by clamping, gluing, embedding etc. The second portion of the contact path element may be slidably received within the holder element. Preferably, it is enclosed within an opening or recess, preferably an elongate channel, of the holder element. 
     In a preferred embodiment, the second portion of the elongate contact path element is received to be guided within a non-conductive enclosure. The enclosure preferably surrounds the contact path element at the second portion at least partly, preferably fully, such that it may be guided with respect to all traverse directions, but remains slidably moveable in longitudinal direction thereof. 
     According to a further preferred embodiment, the contact path element comprises a third section arranged between the first and second section thereof. A spring space is provided within the housing, such that the third section is arranged to be moveable into said spring space in response to a longitudinal motion of the second section. Thus, as, during manufacturing, the slidably received second section of the contact path element moves in longitudinal direction thereof, this may result in a deflection of the contact path element at the third section, such that it may enter the provided free spring space to a varying extent, dependent on the longitudinal motion of the second section. By providing a spring space and moveable third section, it is easily possible to compensate for manufacturing tolerances, such that the connection of the contact path element to the operating circuit can be made reliably, e. g. by soldering. 
     Preferably, the contact path element in the readily manufactured lamp may be spring-loaded to exert a force in longitudinal direction of the second portion thereof. During manufacture, it is preferred that the operating circuit, preferably at a contact surface, is pressed against the contact path element such that the second portion thereof is displaced in longitudinal direction of the second portion. This may lead to a spring-loaded arrangement of the contact path element in respect of the operating circuit, such that the contact path element by its corresponding arrangement presses against the contact surface, ensuring a reliable contact. 
     According to a preferred embodiment of the invention, the contact path element is bent to form an angle. This angle may be formed between the first and second section thereof. Preferably, the angle is formed between the third and second section. The angle may be e.g. 30 to 120° and preferably corresponds at least substantially (e.g. +/−10°) to a right angle of 90°. 
     The contact path element is preferably fixed to a carrier of the operating circuit, such as a leadframe or a printed circuit board (PCB), comprising at least some components of the operating circuit. It is especially preferred that the contact path element is fixed to a contact surface by soldering. A soldering connection may be reliably made in particular when the contact path element is pressed against the contact surface. In order to allow external access of a tool, e.g. for soldering, welding, crimping etc, the holder element preferably comprises an opening allowing access to the fixing position of the contact path element to the operating circuit. 
     The contact path element is preferably a flat, bent element made out of sheet metal. It is further preferred that a plurality of contact path elements are arranged at least substantially in parallel. Further, it is preferred that the contact path element connects the operating circuit to a plug/socket connector provided to be accessible from outside of the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments hereinafter. 
       In the drawings, 
         FIG. 1  shows a perspective view of an embodiment of an automotive HID lamp; 
         FIG. 2  shows a sectional view of the lamp of  FIG. 1  with the section along A . . . A in  FIG. 1 ; 
         FIG. 3  shows an exploded view of the lamp of  FIG. 1 ,  FIG. 2 ; 
         FIG. 4  shows a side view of the lamp of  FIG. 1-3  with a partially cut-away housing; 
         FIG. 5  shows an enlarged partial sectional view of the lamp of  FIG. 1-4  with the section along B . . . B in  FIG. 1 ; 
         FIG. 6  shows a perspective exploded view of parts of the lamp of  FIG. 1-5 ; 
         FIG. 7  shows a perspective view of parts of the lamp of  FIG. 1-6 ; 
         FIG. 8  shows a partial sectional view of the lamp of  FIG. 1-7 ; 
         FIG. 9  shows a sectional perspective view of parts of the lamp of  FIG. 1-8  with the section along A . . . A in  FIG. 1 ; 
         FIG. 10  shows a perspective view of parts of the lamp of  FIG. 1-9 , including an electromagnetic shield. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a lamp  10  including a lamp base  12 , from which a burner  14  protrudes. 
     As visible in particular from the cross-sectional view of  FIG. 2 , the burner  14  is comprised of a burner tube  16  forming a discharge vessel  18  with an enclosed discharge space and an outer bulb  20  arranged around the discharge vessel  18 . The outer bulb  20  and the burner tube  16  with the discharge vessel  18  are made of quartz glass material. Within the discharge space, which comprises a filling of metal halides and Xenon, a first and second electrode are provided. The first electrode is electrically connected to a first, central contact lead  22  extending within the burner tube  16  into the housing  12 . A second electrode is connected to a return contact lead  24  extending in parallel to the longitudinal axis X of the burner  14 . A ceramic tube  26  is arranged around the return contact lead  24  for insulation. 
     The burner  14  is mechanically held relative to the lamp cap housing  12  by a holding ring structure  32  provided around the burner  14 , fixed to a collar of the burner  14  by spot-welded spring tongues. 
     The lamp base  12  comprises a metal outer housing  40 , an inner housing holder element  30 , and a bottom plate  44 . All of the outer housing wall elements  40 ,  44  are made out of aluminum as a metal material of good heat conduction properties. The inner holder element  30  is made out of a plastic material. 
     Within the lamp base  12 , electrical components of a lamp operating circuit  50  are arranged. The lamp operating circuit  50  is supplied with electrical power from an electrical plug/socket connector  52  opening to the side of the lamp base  12 . For use in a motor vehicle headlamp, the lamp  10  is electrically connected to onboard electrical power and to ground via the connector  52 . The lamp operating circuit  50  integrated within the lamp base  12  provides all circuitry required to adapt the voltage supplied at connector  52  to the type of electrical driving voltage and current required for the operation of the burner  14  during ignition, following run-up and steady-state operation. The lamp operating circuit  50  comprises on a printed circuit board  58  and connected thereto circuitry and electrical components for ignition and operation of the lamp  10  as well as a microcontroller for controlling operation of to the burner  14 . 
     As visible from the exploded view shown in  FIG. 3  (where some internal parts within the base are not shown for better understanding), the plastic holder  30  is enclosed within the aluminum housing  40 . As will be explained below, the holder  30  serves for mounting a plurality of components of the lamp operating circuit  50 , such as a transformer and the electrical plug/socket connector  52 . The holder  30  further holds electrical contacts of these components. The holder  30  is substantially box-shaped with side walls  34  and a top wall  38 . The top wall  38 , as shown in  FIG. 2 , is oriented towards the burner  14 , covered by the metal housing  40 . 
     As visible in particular from the cross-sectional view of  FIG. 2 , the burner  14  is mounted at a central opening  28 , and is arranged to protrude quite a distance axially along the longitudinal axis X into the lamp base  12 . The result of the corresponding arrangement of the burner  14  quite deep within the lamp base  12  leads to a reduced light center length (LCL), i.e. distance between the center of the discharge vessel  18  relative to the holding ring  32  comprising position reference elements for relative positioning within a reflector of a motor vehicle headlight unit. 
     As the burner  14  is thus installed to protrude into the lamp cap housing  12 , the electrical contact leads from the burner  14 , namely the central contact lead  22  and return contact lead  24 , also extend into the lamp cap housing  12 . In operation of the lamp  10 , and in particular during ignition, insulation needs to be provided to prevent flashover between the electrical contact leads  22 ,  24  as well as from any of the contact leads  22 ,  24  to components or contact leads of the lamp operating circuit  50  or parts of the lamp cap housing  12 . In order to provide this insulation, a plastic cap  60  is provided, covering the central contact lead  22  and the return contact lead  24  axially. The cap  60  serves to provide electrical insulation, in particular between the central contact lead  22  and return contact lead  24 , but also between the contact leads  22 ,  24  and the metal bottom plate  44 . 
     Components of the lamp operating circuit  50  are arranged on a printed circuit board  58  provided within the lamp base  12 , holding and electrically interconnecting the electrical circuit components provided thereon. The printed circuit board (PCB)  58  with electrical components mounted on a top surface is arranged directly on the bottom plate  44 . Thus, there is close thermal contact between the lamp operating circuit  50  and the bottom plate  44 , so that the bottom plate  44  serves as heat sink. 
     The operating circuit  50  arranged within the base  12  comprises all necessary circuitry, such that the lamp  10  for all modes of operation requires only connection to the onboard voltage of a motor vehicle, which may be supplied at the plug/socket connector  52 . The operating circuit  50  includes an ignitor for supplying a high voltage to the burner  14  for igniting an arc discharge within the discharge vessel  18 . The operating circuit further comprises a driver circuit for generating an alternating current for operation of the burner  14  in a run-up period after ignition and in subsequent steady-state operation. The operating circuit  50  comprises a micro-controller for control of the operation of the components of operating circuit  50  and of the burner  14 . 
     As shown in  FIG. 7 , the plug/socket connector  52  comprises three contacts  62  protruding within a socket cavity  64  formed within the holder element  30 . One of the contacts  62  is a ground contact, connecting the lamp  10  to electrical ground of the vehicle onboard electrical system. The other contacts are provided for a supply voltage (onboard voltage of the vehicle, e.g. 12 V) and for transmitting communication control signals from an electronic control unit (ECU) on board of the vehicle to the micro-controller of the operating circuit  50  and vice versa. 
       FIG. 4-7  show how the electrical contacts  62  of the plug/socket connector  52  are connected to the PCB  58  via contact path elements  70 , which are held by the holder  30 . 
     The contact path elements  70  are flat, elongate metal strips or webs. Corresponding to the three contacts  62  of the plug/socket connector  52 , there are three contact path elements  70  arranged in parallel within the base  12 , extending from the connector  52  to the PCB  58 . The contact path elements  70  are bent roughly L-shaped, as shown in  FIG. 4  (where the holder  30  is not shown),  FIG. 5 . Both ends of the contact path elements  70  are bent to form contact flaps  71   a ,  71   b  for contacting the electrical contacts  62  of the connector  52  and for contacting contact surfaces of the PCB  58 . Each contact flap  71   a  of the contact path element  70  is fixed to one plug contact  62  via spot welding, and each contact flap  71   b  is fixed to one contact surface  72  by soldering. 
     As visible from  FIG. 4 ,  FIG. 5  (where the metal outer housing  40  is not shown), the contact path elements  70  extend from the connector  52  in a first portion  70   a  substantially in parallel to the upper surface of the base  12 , oriented towards the burner (i. e. horizontally in  FIG. 4 ,  FIG. 5 ). The first portion  70   a  of the contact path elements  70  is fixed to the holder  30  by partly embedding the first portion  70   a  of the contact path elements  70  within the plastic material. 
     The contact path elements  70  are bent at an angle of about 90° to continue as a second section  70   b  towards the PCB  58 , i. e. substantially in parallel to the longitudinal axis X of the lamp  10 . The second section  70   b  of the contact path elements  70  is held and guided by the holder  30 , but not fixed thereto. The holder  30  provides an elongate opening, through which the second section  70   b  of the contact path elements  70   a  protrudes, such that each of the metal webs is surrounded by the plastic material of the holder  30  in traverse directions. Thus, the second section  70   b  of the contact path elements  70  is slidably received within the opening of the holder  30 , such that it is movable in longitudinal direction while being guided in traverse direction by the enclosing plastic material. 
     During assembly of the lamp  10 , the assembled PCB  58  is connected to the holder  30  as shown in the exploded view of  FIG. 3 , such that the second contact flaps  71   b  of the contact path elements  70  come to rest on the contact surfaces  72  of the PCB  58 . 
     In order to be able to establish a reliable solder connection, the holder  30  and the contact path elements  70  are pre-assembled with the length of the second section  70   b  designed for an interference fit, i. e. longer than necessary for an exact 90° bend between the first section  70   a  and second section  70   b  of the contact path elements  70 . Thus, before assembly, the contact flaps  71   b  extend out of the holder  30  to protrude a small distance below. As the PCB  58  is fitted, a force acts longitudinally on the second section  70   b  of a contact path element  70 , such that this section of the contact path elements  70  slides longitudinal within the guiding fit of the holder  30 . Within the base  12 , the holder  30  leaves a spring space  74  free, into which a third section  70   c  of the contact path elements is received as it is deflected by the force exerted on the second section  70   b  of the contact path elements  70 . 
     By providing the mentioned oversize, slidable reception and spring space  74 , a clamping fit of the contact flaps  71   b  on the contact surfaces  72  of the PCB  58  is achieved, where a spring force of the deflected third section  70   c  of the contact path elements  70  achieves a pressing force, pressing the contact flaps  71   b  onto the contact surfaces  72 . Subsequently, the solder connection is made. 
     The holder  30  comprises an opening  45  which allows access to the contact flaps  71   b  and contact surfaces  72  for soldering. 
     As already mentioned, one of the contacts  62  provided at the connector  52  is an electrical ground contact, connected to electrical ground of the motor vehicle. As shown in  FIGS. 6, 8 , a contact spring  76  is provided in one piece with one of the contact path elements  70  serving as the electrical ground contact, the contact spring  76  being provided to establish an electrical ground connection to the metal housing  40 . 
     The holder  30  includes an opening  78  provided within the top wall  38 . The contact spring  76  is fixed to the holder  30  and extends through the opening  78  up to the metal housing  40 . 
     As shown in the partial views of  FIGS. 8, 9 , the top surface  80  of the base  12  is a metal sheet element which is part of the metal housing  40  and is made from aluminum. A contact sheet element  82  is arranged flat underneath the top surface  80  of the metal housing  40  in close contact therewith. The contact sheet element  82  is a thin piece of sheet metal made from a steel material, considerably thinner than the aluminum sheet material of the top surface  80 . 
     The burner holding ring  32  includes a flange  33  extending downwardly up to the top surface  80 . The burner holding ring  32  is fixed to the base  12  by means of a crimping connection of the top surface  80  of the metal housing  40  with the flange  33 . As shown in  FIG. 9 , the sandwich structure formed of the steel material of the contact sheet element  82  and the aluminum material of the top surface  80  of the metal housing  40  is bent at the central opening  28  for the burner  14  to surround the flange  33  of the burner holding ring  32 . The thus formed crimping connection extends around the substantially circular opening  28  in the top surface  80  provided for the burner  14  and is effective to both fix the flange  33 , and thereby the burner holding ring  32  to the top surface  80 , and also to provide a close mechanical (and thereby also electrical) connection between the contact sheet element  82  and the top surface  80  of the metal housing  40 . 
     As shown in  FIG. 6 ,  FIG. 8 , the contact spring  76  provides two contact fingers  84  which bear against the lower surface of the contact sheet element  82  in a clamping fit. Thus, the electrical ground connection provided at the connector  52  is brought into electrical contact with the metal housing  40  via the contact spring  76  and the contact sheet element  82 . 
     As already explained, the operating circuit  50  comprises an ignitor for igniting an electrical arc discharge within the discharge vessel  18 . The ignitor includes an ignition transformer  54  as shown in  FIG. 2 , arranged within an insulation chamber  42  with side walls formed integrally with the holder  30 . The ignition transformer  54  is embedded, for purposes of electrical insulation, within an insulation compound  43 . 
     The insulation compound  43  is a silicone insulation compound, which is filled into the insulation chamber  42  in upside-down orientation, as e.g. shown in  FIG. 6 . The transformer  54  is placed within the insulation chamber  42 , and the insulation compound  43  is filled into the chamber  42  in a liquid form. The holder  30  including the filled insulation chamber  42  is then placed into an oven for a heat curing treatment of the insulation compound  43 , such that the insulation compound  43  solidifies. 
     During filling of the insulation chamber  42  in the upside-down orientation as shown in  FIG. 6 , any amounts of the liquid insulation compound  43  possibly leaking from the insulation chamber  42  into the interior of the holder  30  are retained by a retention wall  46  provided around the central opening  28 . Thus, leaked amounts of the insulation compound  43  will not leak through the opening  28  onto the—in the upside-down orientation of  FIG. 6 —bottom surface of the holder  30 , i.e. onto the top surface (in  FIG. 2 ) of the base  12 , exposed to heat and radiation from the burner  14 . Thus, evaporation of silicone, and in particular silicone entering the front parts of the lamp  10  and the reflector, into which the lamp  10  will be mounted, is effectively prevented. 
     The central opening  28  in the top wall  38  of the holder  30 , through which the burner  14  protrudes, is connected with a further opening in the top wall  38 , through which the return contact  24  enters the base  12 . The retention wall  46  is arranged to surround both openings. Further, the top wall  38  of the holder  30  includes, as already explained, an opening  78  for the ground contact spring  76 . The opening  78 , as shown in  FIG. 8 , is also surrounded by raised retention walls  48 , extending, in the same way as the retention wall  46  around the central opening  28 , perpendicularly from the top wall  38  of the holder  30 . Thus, even larger amounts of leaked insulation compound  43  are safely retained within the holder  30  until the curing treatment. During the curing treatment, leaked compound  43  within the interior of the holder  30  will solidify as well, such that there is no further risk of silicone entering the front portions of the lamp  10 . 
     As shown in the figures, in particular  FIG. 2 , the packaging of electrical components and contacts within the base  12  is particularly dense, such that the distances between the electrical components are small. In order to reduce the risk of EMI, in particular from the ignitor components, such as the ignition transformer  54 , a metal shield  36 , as shown in  FIG. 10 , is arranged within the base  12 . The metal shield  36  is arranged substantially in parallel to the top and bottom surfaces of the base  12 , e.g. substantially horizontally, as shown e.g. in  FIG. 2 ,  FIG. 4 . The metal shield  36  is arranged to partly cover the PCB  58 , and in particular to separate components on the PCB  58  from the ignition transformer  54 . Further, as shown in  FIG. 2 , the metal shield  36  is also arranged to partly shield the plug/socket connector  52  and the contact leads  70  from further components within the base  12 , in order to prevent EMI from spreading within the base  12  via these connections. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
     Variations of the disclosed embodiment can be understood and effected by those skilled in the art in practising the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” or “including” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.