Patent Publication Number: US-6710545-B2

Title: Discharge lamp apparatus having directly coupled lamp and electronic controller

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-206203 filed on Jul. 6, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a discharge lamp apparatus that uses a discharge lamp as a light source, and particularly to an apparatus in which an electronic controller unit for applying a voltage to the discharge lamp is directly coupled with the discharge lamp. 
     BACKGROUND OF THE INVENTION 
     A discharge lamp apparatus that uses a discharge lamp as a light source is used as a vehicle headlight. An electronic controller unit that generates and controls a voltage applied to the discharge lamp includes a DC/DC converter for transforming an output voltage by switching an input voltage by a power device, a high voltage generation circuit for generating, from the output voltage of the DC/DC converter, a high voltage applied when lighting of the discharge lamp is initiated, and the like. 
     When the temperature of electronic circuit components forming the controller unit rises, it is likely that, for instance, the soldered part of the circuit components melt and the circuit components operate erroneously. In the discharge lamp apparatus disclosed in JP-A-2000-235809, a part of a metallic heat radiator thermally coupled with a circuit substrate mounting circuit components thereon is exposed outside a headlight so that the heat generated by the discharge lamp and the circuit components may be radiated to the outside of the headlight through the metallic heat radiator. 
     In the discharge lamp apparatus disclosed in JP-A-2000-235809, an igniter part and a lighting device need be connected by a harness. This increases the number of component parts, complicates assembling work and adds manufacturing cost. 
     It is therefore proposed to directly couple and electrically connect the discharge lamp and the controller unit. However, if the discharge lamp and the controller unit are directly coupled and the controller unit is disposed near the discharge lamp, the internal temperature of the controller unit rises due to heat transferred or radiated from the discharge lamp and the heat generated by the controller unit itself. This is likely to cause erroneous operation of the circuit components in the controller unit. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a discharge lamp apparatus that uses no high voltage wire nor high voltage connector and suppress rise of temperature of an electronic controller unit. 
     In a discharge lamp apparatus according to the present invention, a discharge lamp and an electronic controller unit for applying a voltage to the discharge lamp are directly coupled with and electrically connected to the discharge lamp. Therefore, a high voltage connector and a high voltage wire for connecting the discharge lamp and the controller unit are not necessitated. 
     Preferably, a second casing mounting a power device of a DC/DC converter has a thermal conductivity higher than that of a first casing coupled with the discharge lamp. As a result, heat generated by the discharge lamp is less likely to be transferred from the first casing to the second casing, and the heat of the discharge lamp is less likely to be transferred circuit components mounted in the second casing. 
     In addition, heat generated by the power device of the DC/DC converter is more likely to be radiated to the outside of the second casing from the second casing that has the thermal conductivity higher than that of the first casing. Because the power device of the DC/DC converter generate more heat among the controller unit, the heat generated by the power device is readily radiated from the second casing to the outside of the second casing, thus suppressing rise of temperature of the circuit components in the controller unit including the power device. Thus, erroneous operation of the circuit components is prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
     FIG. 1 is a sectional view showing a headlight using a discharge lamp apparatus according to the first embodiment of the present invention; 
     FIG. 2 is a schematic sectional view showing a discharge lamp and a controller unit in the first embodiment; 
     FIG. 3 is a circuit diagram showing the controller unit in the first embodiment; 
     FIG. 4 is a schematic sectional view showing a discharge lamp and a controller unit in the second embodiment; 
     FIG. 5 is a schematic sectional view showing a discharge lamp and a controller unit in the third embodiment; 
     FIG. 6 is a schematic sectional view showing a discharge lamp and a controller unit in the fourth embodiment; 
     FIG. 7 is a schematic sectional view showing a discharge lamp and a controller unit in the fifth embodiment; 
     FIG. 8 is a schematic sectional view showing a discharge lamp and a controller unit in the sixth embodiment; and 
     FIG. 9 is a schematic sectional view showing a discharge lamp and a controller unit in the seventh embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various embodiments of the present invention is described hereinbelow with reference to the drawings. 
     (First Embodiment) 
     The first embodiment of the present invention in which a discharge lamp apparatus is applied as a headlight of a vehicle is shown in FIG. 1. A headlight  10  includes a headlight casing  11 , a reflector  20 , a discharge lamp  30  and an electronic controller unit  40 . The casing  11  includes a casing body  12 , a lens  13  and a cover  14 , and accommodates the reflector  20 , discharge lamp  30  and the controller unit  40 . The discharge lamp  30  and the controller unit  40  form a discharge lamp apparatus. A power supply cord  90  connects to the controller unit  40  through a connector  91  and to a battery power source  15  shown in FIG. 3 through a connector  92 . When a driver turns on a switch  16 , the voltage of the battery power source  15  is supplied to the controller unit  40  so that a voltage for activating the discharge lamp  30  is generated. 
     As shown in FIG. 1, the reflector  20  is supported movably by the casing body  12  through a supporting member (not shown) that has a mechanism capable of adjusting the optical axis of the reflector  20 . The reflector  20  is made of resin and shaped configured in a bowl shape. A reflector  20  is formed with a reflection layer on its concave reflection surface to reflect light of the discharge lamp  30  forward. 
     The discharge lamp  30  is fit in a through hole  20   a  of the reflector  20 . A shape  32  is provided to shut off direct light of the discharge lamp  30  projected in the forward direction. Metallic support fittings  22  and  23  are attached to the upper part and lower part of a supporting part  21  formed around the outer periphery of the through hole  20   a . A spring  25  is configured in a U-shape and rotatably attached to the lower metallic fitting  22 . Both ends of the U-shape of the spring  25  are hooked to the upper metallic fitting  23  so that the spring  25  presses the flange  31   a  of the connector part  31  of the discharge lamp  30  to the reflector  20  around the outer periphery of the through hole  20   a.    
     The controller unit  40  includes an electric circuit for supplying a voltage to the discharge lamp  30 . Under the condition that the discharge lamp  30  and the controller unit  40  are assembled as shown in FIG. 1, the discharge lamp  30  and the controller unit  40  are held contactless with the casing  11  and movable relative to the casing. Therefore, the optical axis of the discharge lamp  30  is adjustable manually or automatically. 
     As shown in FIG. 2, the casing  41  of the controller unit  40  includes a resin casing  42  which is the first casing and a metal casing  44  which is the second casing, and accommodates circuit components therein. The thermal conductivity of the metal casing  44  is higher than that of the resin casing  42 . Preferably, the metal casing  44  is made of a material that has a high thermal conductivity of more than 20 W/m·K, for instance, aluminum (thermal conductivity ≈200 W/m·K), aluminum alloy (thermal conductivity ≈72 W/m·K), iron (thermal conductivity ≈50 W/m·K), copper (thermal conductivity ≈400 W/m·K) or magnesium alloy (thermal conductivity ≈65 W/m·K). Because the controller unit  40  is moved to adjust the optical axis through the reflector  20 , aluminum alloy that is light in weight is more preferable for simplifying the optical axis adjusting mechanism. The resin casing  42  is coupled and in contact with the connector part  31  of the discharge lamp  30 . A coil  61 , an electrolytic capacitor  62  and a high voltage coil  81  are electrically connected to terminals  43  insert-molded in the resin casing  42 . 
     A circuit board  55  and a plate member  75  made of an insulating material such as aluminum nitride are bonded to the inside bottom surface or the inside opposing surface of the metal casing  44  that faces the discharge lamp  30 . The thermal resistance of the plate member  75  is lower than that of air. A power MOS transistor  72  of a DC/DC converter  70  is soldered to the plate member  75 . The power MOS transistor  72  used as the power device is in the form of a bare chip which has its terminal exposed to the side of metal casing  44 . 
     As shown in FIG. 3, the controller unit  40  includes a control circuit  50 , H-bridge circuit  51 , filter circuit  60 , DC/DC converter  70  and high voltage generation circuit  80 . The control circuit  50  comprises semiconductor devices which control circuit components in the controller unit  40 . A driver  52  turns on and off the power MOS transistor of the H-bridge circuit  51  based on the switching signal applied from the control circuit  50  to inverter-control the H-bridge circuit  51  so that the voltage applied to the discharge lamp  30  is inverted into a pulse waveform. The control circuit  50 , H-bridge circuit  51  and driver  52  are mounted on the circuit substrate  55 . The filter circuit  60  comprises the coil  61  and the electrolytic capacitor  62  and smoothes the power source voltage supplied from the battery power source  15 . 
     The DC/DC converter  70  comprises a DC/DC transformer  71 , power MOS transistor  72  which is a power device, diode  73  and capacitor  74  to boost the power source voltage. The control circuit  50  controls the duty ratio of the switching signal applied to the power MOS transistor  72  to control the electric power supplied to the discharge lamp  30  from the DC/DC converter  70 . The diode  73  and the capacitor  74  rectify and smooth the induced voltage generated at the secondary coil side of the DC/DC transformer  71 . The high voltage generation circuit  80  comprises a high voltage coil  81 , capacitor  82  and thyristor  83 . The high voltage coil  81  generates a starting voltage for initiating lighting of the discharge lamp  30 . The capacitor  82  charges the current supplied to the primary coil side of the high voltage coil  81 . The thyristor  83  controls discharging of the capacitor  82 . 
     The discharge lamp  30  and the power MOS transistor  72  generate a large amount of heat during lighting operation of the discharge lamp  30 . However, because the thermal conductivity of the resin casing  42  is low, heat generated by the discharge lamp  30  is less likely to transfer from the resin casing  42  and the metal casing  44 . Further, because the metal casing  44  has a high thermal conductivity, heat generated by the power MOS transistor  72  is radiated efficiently from the metal casing  44  to the outside of the casing  44 . As a result, it is less likely that the heat generated by the discharge lamp  30  and the power MOS transistor  72  is transferred to the circuit components provided inside the controller unit  40 . Thus, temperature rise of the circuit components inside the controller unit  40  including the power MOS transistor  72  is limited, and erroneous operation of the circuit components are restricted. 
     The power MOS transistor  72  is disposed on the inside opposing surface  44   a  of the metal casing  44  in a manner to face the discharge lamp  30 , and spaced apart from the discharge lamp  30 . Further, the thermal resistance of the plate member  75  is lower than that of air present between the power MOS transistor  72  and the discharge lamp  30 . As a result, the heat generated by the power MOS transistor  72  is transferred to the metal casing  44  from the plate member  75  and radiated from the metal casing  44  to the outside of the same. 
     (Second Embodiment) 
     In the second embodiment shown in FIG. 4, the power MOS transistor  72  of the DC/DC converter is in the form of a bare chip or a resin-molded chip in which the terminal is not exposed on the surface contacting the metal casing  44 . As a result, the power MOS transistor  72  is attached in direct contact to the metal casing  44 . 
     (Third Embodiment) 
     In the third embodiment shown in FIG. 5, the casing comprises the box-shaped resin casing  42  as the first casing and the plate-shaped metal casing  44  as the second casing. The resin casing  42  is coupled with the connector part  31  of the discharge lamp  30 , and the circuit board  55  and the power MOS transistor  72  are attached to the metal casing  44 . 
     (Fourth Embodiment) 
     In the fourth embodiment shown in FIG. 6, the power MOS transistor  72  is not attached to the inside opposing surface  44   a  of the metal casing  44  facing the resin casing  42  but is attached to an inside side surface  44   b.    
     (Fifth Embodiment) 
     In the fifth embodiment shown in FIG. 7, the resin casing  42  is provided as the first casing only around the connector part  31  of the discharge lamp  30 . The metal casing  44  is formed as the second casing with two metal casings  122  and  123 . The power MOS transistor  72  is attached to the metal casing  123  which is on the same plane as the resin casing  42 . 
     (Sixth Embodiment) 
     In the sixth embodiment shown in FIG. 8, the metal casing  44  as the second casing has a surface inclined relative to the resin casing  42 . The power MOS transistor  72  is attached to the inclined surface. 
     (Seventh Embodiment) 
     In the seventh embodiment shown in FIG. 9, the power MOS transistor  72  is mounted on the circuit board  55 . The metal casing  44  is formed with an upper air passage hole  45  and a lower air passage hole  46  as air vents, so that air readily flows in the casing  41 . In the seventh embodiment, in particular, because the air vents are formed at both upper and lower parts of the metal casing  45 , heated air readily flows out to the outside of the casing  41  through the upper air passage hole  45  and outside air readily flows in the inside of the casing  41  through the lower air passage hole  46 . As a result, temperature of air in the casing  41  is restricted from rising. Further, the air flowing through the casing  41  cools the power MOS transistor  72 . 
     In the above embodiments of the present invention, the discharge lamp  30  is attached to the resin casing having a low thermal conductivity and the power MOS transistor of the DC/DC converter  70  is attached to the metal casing having a thermal conductivity higher than that of the resin casing. As a result, heat of the discharge lamp  30  is restricted from transferring to the circuit components in the casing unit that includes the power MOS transistor of the DC/DC converter. In addition, heat of the power MOS transistor is efficiently radiated from the metal casing to the outside of the metal casing. Thus, temperature of the circuit components in the controller unit including the power MOS transistor is restricted from rising, and erroneous operation of the circuit components is also restricted. 
     In the above embodiment, the first casing which connects to the discharge lamp  30  is made of resin and the second casing which mounts the power MOS transistor is made of metal. However, the materials are not limited as long as the thermal conductivity of the second casing is higher than that of the first casing.