Abstract:
There is a vehicle headlamp in a multibeam mode comprising: a reflecting mirror for reflecting light emitted from a discharge tube having a single light emitting section; and a shield for blocking off light directly emitted forward and light emitted to the lower part of the reflecting mirror out of the light emitted from the discharge tube, wherein the headlamp includes a rotationally moving device for three-dimensionally moving the light emitting section of the discharge tube to any position of the reflecting mirror, which is suitable for low-beam or high-beam, by eccentrically rotating the discharge tube to move back and forth; and a rotation controller for controlling the rotation of the rotationally moving device. The headlamp can be used in several beam modes using a conventional reflection mirror and a discharge tube.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a vehicle headlamp, and more particularly relates to a vehicle headlamp having a mechanism that allows the headlamp to be used in several beam modes using a discharge tube having a single light emitting section. 
   2. Description of the Related Art 
   At present, so-called projector-type or multireflector-type headlamps dominate the vehicle headlamp market, which concentrate light with high precision by arranging a reflecting mirror around a halogen lamp (iodine bulb) which is close to a point source with power consumption of 35 to 60 watts and high efficiency of about 20 lumens/watt. Two standards are set for the projector-type headlamps: PE (polyellipsoid) and DE (three-dimensional ellipsoid) type. The multireflector-type headlamps use a MS (multisurface) type. 
     FIG. 6  is an external view of a conventional vehicle headlamp  1 .  FIGS. 7A  to  7 C are sectional views of the vehicle headlamp  1 , in which  FIG. 7A  shows a case in which a halogen lamp  2  is used as a light source and  FIG. 7B  shows a case in which a discharge tube  3 , such as a xenon lamp, is used as a light source, and  FIG. 7C  is an enlarged view of a filament section of the halogen lamp  2 . The headlamp  1  in  FIG. 7A  is a so-called projector-type or multireflector-type headlamp, in which two light emitting sections (filament)  52  and  50  of the halogen lamp (iodine bulb)  2  which is close to a point source with power consumption of 35 to 60 watts and high efficiency of about 20 lumens/watt, that is, a high-beam light emitting section  52  and a low-beam light emitting section  50  covered with a shade  51  are arranged in line in the direction of arrow Z (back and forth in a state in which the headlamp  1  is mounted to the vehicle), around which a reflecting mirror  55  is disposed, thereby concentrating light with high precision. 
   In the headlamp  1  in  FIG. 7A , light beams that are emitted from the two high-beam light emitting section  52  and low-beam light emitting section  50  covered with the shade  51  are sent toward the reflecting mirror  55  in the direction of X (laterally in a state in which the headlamp  1  is mounted to the vehicle) and in the direction of Y (vertically in a state in which the headlamp  1  is mounted to the vehicle), respectively, and are reflected in the direction of Z by the reflecting mirror  55 . 
   The halogen lamp  2  used in the headlamp  1  lights up by applying a voltage as low as 12V or 24V, thus requiring no special insulation and having an average operating time of 400 hours. Several types of specifications, called H-1 type, HB-1 type, H-4 type, HB-4 type, HB-5 type, H-7 type and so on, are set in shape, for each of which the shapes and sizes of a base mounting section (lamp holder) on the side of illuminating apparatus and a flange base on the side of the halogen lamp are standardized. 
   Conventionally, the low beam and high beam in the headlamp using the halogen lamp were switched by selecting two dedicated halogen lamps which are arranged at approximately the center of the reflecting mirror divided for high beam and low beam; however, recently, the high-beam light emitting sections  52  and the low-beam light emitting section  50  covered with a shade are provided side by side in one halogen lamp, as in the H-4 type shown in  FIG. 7A , and are selected for illumination. More specifically, for high beam emission, only the high-beam light emitting section  52  is lit up and, for low beam emission, only the low-beam light emitting section  50  covered with the shade  51  is lit up to block off light on the side of the shade  51  and alter the reflection by the reflecting mirror, thus controlling light distribution. 
   On the other hand, in the halogen lamp  2  used in the headlamp  1 , as shown in  FIG. 7C , the relative position of the high-beam light emitting section  52  and the low-beam light emitting section  50  covered with a shade is deviated from each other. Specifically, the high-beam light emitting section  52  and the low-beam light emitting section  50  are separated, at the center point, by L 2  (about 6.5 mm) in the Z direction and by L 1  (about 1.2 mm) in the Y direction. Consequently, the reflecting surface of the reflecting mirror  55  is set to reflect light in a predetermined direction at each position of the high-beam light emitting section  52  and the low-beam light emitting section  50 . More specifically, the high-beam light emitting section  52  and the low-beam light emitting section  50  are selectively lit up, wherein, when the high-beam light emitting section  52  is lit up, light beams IH 1  and IH 2  are reflected by the reflecting mirror  55  to irradiate a distance, and when the low-beam light emitting section  50  is lit up, only a light beam IL 1  is reflected by the reflecting mirror  55  to become a downward light beam and irradiate a short distance. 
   There is also provided a discharge tube, such as a xenon lamp, as a light source taking the place of the halogen lamp  2 . In this discharge tube, although the voltage applied at initial lighting is as high as about 20,000V, highly efficient 100±15% lumens/watt is provided, thus providing luminous flux twice as large as that of the halogen lamp. Also, the power consumption is only about 35 W and the operating time is more than four times as long as that of the halogen lamp. Accordingly, it is the most suited to save energy and ideal for a vehicle headlamp. The headlamp, particularly, the vehicle headlamp must be constructed to switch low-beam and high-beam; however, it is structurally difficult for the present discharge tube  3  to include two light emitting sections in the lamp itself, as in the halogen lamp  2  of the H-4 type. 
   Also, there is a problem of spacing in that separate two discharge tubes are provided near the center of the reflecting mirror, as in the conventional type, and it is also difficult to construct the reflecting mirror. Furthermore, it is relatively expensive in cost. Accordingly, even if the conventional discharge tube  3  is arranged as in  FIG. 7B , the conventional switching of low-beam and high-beam cannot be performed, so that when a light emitting section  53  of the discharge tube  3  is arranged at a position where the high-beam light emitting section  52  of the halogen lamp  2  is to be arranged, the light beams IH 1  and IH 2  are reflected by the reflecting mirror  55  to irradiate only a distance. 
   There is provided a headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, which solves the above problems. Such a headlamp has a structure including a drive unit K for sliding a shade  67  for shielding a light emitting section  65  of a discharge tube  64  disposed at a base  61  in the direction of arrow X along the axis Z of the discharge tube  64 , as shown in  FIGS. 8A and 8B .  FIG. 8A  is a front view showing the structure of the discharge tube  64  and the base according to an embodiment of the invention disclosed in the above-mentioned application in a low-beam mode and  FIG. 8B  is a front view of the same in a high-beam mode. A leg  67   b  of the shade  67  is connected through the base  61  to a moving iron  69  of a solenoid  68  secured to the back of the base  61  with a rod  66  and so on. The moving iron  69  is biased at all times by a spring  60 , so that when the solenoid is inoperative, a shielding surface  67   a  of the shade  67  stands in the position of the light emitting section  65  to block off the light from the discharge tube  64  partly, thus providing low-beam light distribution. The coil of the solenoid  68  is energized to draw the moving iron  69  against the stress of the spring  60  and to slide the shade  67 . When the shielding surface  67   a  gets out of position of the light emitting section  65  of the discharge tube  64 , light is radiated from the light emitting section  65  in almost all directions to provide high-beam light distribution. 
   The above method, however, has the following problems: The high-beam light emitting section  52  and the low-beam light emitting section  50  are separated at the center point by L 2  in the Z direction and by L 1  in the Y direction, as described above. However, in the headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, the shade  67  for shielding the light emitting section  65  is only slid in the direction of arrow X along the axis Z of the discharge tube  64 . Consequently, a light emitting section can only be placed at the position of one of the high-beam light emitting section  52  and the low-beam light emitting section  50 . 
   On the other hand, the reflecting surface of the reflecting mirror  55  is shaped to reflect light in a predetermined direction at each position of the high-beam light emitting section  52  and low-beam light emitting section  50 . Accordingly, the conventionally used reflecting mirror cannot be used but a special reflecting mirror is required to irradiate a predetermined position with light, thus increasing the cost for the headlamp. Also, the standard for vehicle parts is strictly decided; for example, the shape of the reflecting mirror is standardized, as mentioned above, in which the versatility of possible shapes, sizes, installation spaces thereof is low, thus being limited in design. 
   Also, in the headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, the moving iron  69  of the solenoid  68  is secured to the back of the base  61  with the rod  66  and so on. The moving iron  69  is biased at all times by the spring  60 . Therefore, a mechanism for moving the light emitting section  65  of the discharge tube  64  or the shade  67  must be long, thus causing various limitations to enclose such a mechanism in the standardized reflecting mirror. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a vehicle headlamp in which the above problems are solved and which can be used in several beam modes using a conventional reflection mirror and a discharge tube. 
   In order to achieve the above object, in a vehicle headlamp according to the present invention, a multibeam mode vehicle headlamp is equipped with a reflecting mirror for reflecting light emitted from a discharge tube having a single light emitting section and a shield for blocking off light directly emitted forward and light emitted to the lower part of the reflecting mirror out of the light emitted from the discharge tube having the single light emitting section. The head lamp includes a rotationally moving device for three-dimensionally moving the light emitting section of the discharge tube having the single light emitting section to any position of the reflecting mirror, which is suitable for low-beam or high-beam, by eccentrically rotating the discharge tube to move back and forth; and a rotation controller for controlling the rotation of the rotationally moving device. 
   In the vehicle headlamp according to the present invention, preferably, the rotation controller includes a drive unit for switching the rotating direction of the rotation axis for eccentric rotation, a timer circuit for controlling the rotation time of the rotation axis, and a switching circuit for switching the polarity of a signal applied to the rotation controller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially sectional view illustrating a discharge tube of a vehicle headlamp and a mechanism for moving the discharge tube according to an embodiment of the present invention; 
       FIGS. 2A  to  2 C are explanatory views of the discharge tube and a shade for covering it, in which  FIG. 2A  is a schematic side view of a control section of the discharge tube,  FIG. 2B  is a side view of the shade, and  FIG. 2C  is a side view of the control section having the shade covered thereon; 
       FIGS. 3A and 3B  illustrate a moving operation of a light emitting section of the discharge tube, wherein  FIG. 3A  is a top view of a rotationally moving section and  FIG. 3B  is a side view thereof; 
       FIGS. 4A and 4B  show electrical connections for supplying power to a conventional vehicle headlamp, wherein  FIG. 4A  shows a positive control system and  FIG. 4B  shows a negative control system; 
       FIG. 5  is a schematic circuit diagram showing an embodiment of a rotation controller and connections with its peripheral devices; 
       FIG. 6  is an external view of the conventional vehicle headlamp; 
       FIGS. 7A  to  7 C are sectional views of the vehicle headlamp, in which  FIG. 7A  shows a case in which a halogen lamp is used as a light source and  FIG. 7B  shows a case in which a discharge tube is used as a light source, and  FIG. 7C  is an enlarged view of a filament section of the halogen lamp; and 
       FIGS. 8A and 8B  show a structure of the discharge tube and the base of the conventional vehicle headlamp, in which  FIG. 8A  is a front view thereof in a low-beam mode and  FIG. 8B  is a front view thereof in a high-beam mode. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of a headlamp according to the present invention will be specifically described hereinbelow with reference to the drawings. The headlamp according to the present invention principally relates to a vehicle headlamp. Since a discharge tube  3 , and a reflection mirror and a lens (both are now shown), etc., which are used here, are well known in the art, and a headlamp using an existing halogen lamp, as shown in  FIG. 6 , can be used, a description thereof will be omitted and only a low-beam/high-beam switching mechanism of the discharge tube  3  and its controller will be described. 
     FIG. 1  is a partially sectional view showing a discharge tube  3  of a vehicle headlamp and a mechanism for moving the discharge tube  3  according to the embodiment of the present invention (hereinafter, a section shown in  FIG. 1  is referred to as a discharge tube control section A for simplifying explanation). The discharge tube control section A includes a rotating mechanism B, a link mechanism C, a light source D and a main-body casing E. The rotating mechanism B includes a motor  9  and gears  11 ,  12 ,  13  and  14  enclosed in a casing  6  of the main-body casing E. 
   The link mechanism C includes a rotating body  10  connected to the shaft of the gear  13  and a cylindrical rotationally moving section  5 . The light source D includes the discharge tube  3  and a shade  51 , which is not shown in  FIG. 1  but is shown in FIG.  2 B. The main-body casing E includes the casing  6  ( 6   a  and  6   b ) and a fixing section  4 . A controller for rotating the motor  9  and a power source for supplying power to the discharge tube  3  are not shown in FIG.  1 . 
   The casing  6  of the main-body casing E is formed of the casing box section  6   b  for housing the rotating mechanism B and the casing cylinder section  6   a  for housing the rotationally moving section  5 . The fixing section  4  is secured to the casing cylinder section  6   a,  and has a projection  4   a  for attaching a shade  51 , which will be described later, on the side thereof. The main-body casing E is secured with the fixing section  4  from the exterior of a reflecting mirror (not shown) using a metal spring or the like so that a light emitting section  53  of the discharge tube  3  is placed in position, which will be described later. 
   The gear  11  in the rotating mechanism B is fitted to the rotation axis of the motor  9  and is rotated as the motor  9  rotates, as will be described later. The external gear of the gear  11  is connected to the internal gear of the gear  14 , and the gear  14  is connected to the gear  12 . The gear  12  is connected to the gear  13 , to which the rotation of the motor  9  is transmitted with the speed decreased. 
   The rotationally moving section  5  of the link mechanism C is housed in the casing cylinder section  6   a  such that it can be rotated and moved in the direction shown by arrow Z while having contact with the inner wall thereof. Furthermore, the rotating body  10  is housed in the rotationally moving section  5 . The rotating body  10  is fitted to and projecting from the rotation axis of the gear  13  (the central axis of rotation is denoted by reference symbol Q 0 ), from the side of which a pin  8  projects. A slide groove  7  is formed with a slope in the inner wall of the rotationally moving section  5 , into which the pin  8  is fitted so as to slidably move therein. 
     FIGS. 2A  to  2 C are explanatory views of the discharge tube  3  and the shade  51  for covering it, in which  FIG. 2A  is a schematic side view of the discharge tube control section A,  FIG. 2B  is a side view of the shade  51 , and  FIG. 2C  is a side view of the discharge tube  3  of the discharge tube control section A having the shade  51  covered thereon. In  FIGS. 2A  to  2 C, the mounting directions shown by arrows X, Y and Z are the same as those shown in  FIGS. 7A  to  7 C. The shade  51  is cylindrical in shape, having an inner diameter sufficient to avoid contact with the discharge tube  3  even when the discharge tube  3  rotates, as will be described later, into which the discharge tube  3  is fitted from a rear  51   c . Moreover, an umbrella-shaped shielding section  51   a  and a canaliculated shielding section  51   b  are formed at the end and bottom thereof, respectively, for blocking off the light. It is recommended that the shielding sections  51   a  and  51   b  be made of a light-blocking material, such as a thin metal plate formed by stamping, a heat-resistant synthetic resin or ceramics. 
   The shade  51  has a notch  51   d  formed at the rear  51   c  thereof. When the notch  51   d  is rotationally fitted to the projection  4   a  formed on the side of the fixing section  4 , the shade  51  is secured to the fixing section  4 . Specifically, the shade  51  is attached to the headlamp in a fixed direction (in the direction in which the shielding section  51   b  is positioned lower than the discharge tube  3 ). Of light emitted from the light emitting section  53  of the discharge tube  3 , which is rotationally moved as will be described later, light emitted forward (in the direction shown by arrow +Z) and downward is blocked off. 
   The discharge tube  3  of the light source D is fitted in a base  61  disposed on the rotationally moving section  5  such that it projects from the rotationally moving section  5 . The base  61  is disposed such that when the discharge tube  3  is fitted, the central axis Q 1  of the light emitting section  53  is eccentric to the rotational central axis Q 0  of the rotating body  10 . 
   A reflecting mirror (not shown), in which the discharge tube control section A is to be enclosed, has a well-known structure for reflecting light in predetermined directions when the light emitting section  53  is positioned at the position of the high-beam light emitting section  52  or at the position of the low-beam light emitting section  50 . More specifically, the reflecting mirror has a reflecting surface and a lens formed such that when the light emitting section is lit up at the position of the high-beam light emitting section  52 , the light reflected forward from the reflecting mirror goes in the distance without diffusing in all directions and, when the light emitting section is lit up at the position of the low-beam light emitting section  50 , the light reflected forwardly from the reflecting mirror diffuses laterally and downwardly and does not go in the distance. Accordingly, in the headlamp that houses inside the reflecting mirror the discharge tube control section A having the shade  51  fixed thereto, when the light emitting section  53  of the discharge tube  3  is moved to the position of the high-beam light emitting section  52  and lit up, the lower part of light reflected forwardly from the reflecting mirror is blocked off and goes in the distance without diffusing downward, the direction reversed by the reflecting mirror, and laterally. 
   In order to provide an easy understanding of the present invention, the operation of the link mechanism C will be described with reference to  FIGS. 3A and 3B .  FIGS. 3A and 3B  illustrate the operation of the rotationally moving section  5  in which the light emitting section  53  of the discharge tube  3  is moved to the positions of the high-beam light emitting section  52  and the low-beam light emitting section  50  of the headlamp  1 , which are shown in FIG.  7 A.  FIG. 3A  is an explanatory view seen from the top of the rotationally moving section  5  and  FIG. 3B  is an explanatory view seen from the side thereof. In  FIGS. 3A and 3B , the rotation axis of the rotationally moving section  5  is denoted by reference symbol Q 0 , and the rotation axis of the light emitting section  53  of the discharge tube  3  is denoted by reference symbol Q 1 , as in FIG.  1 . The moving directions Y and Z and moving distances L 1  and L 2  of the light emitting section  53  are used as in  FIGS. 7A  to  7 C. 
   As shown in  FIG. 7C , the light emitting section  50  is lit up for low-beam emission. Accordingly, when the discharge tube  3  is used, the light emitting section  53  is positioned at the position of the light emitting section  50 . More specifically, in  FIG. 3A , the center ( 53   a ) of the light emitting section  53  is positioned at point R 1 . Similarly, the light emitting section  52  is lit up for high-beam emission. Accordingly, when the discharge tube  3  is used, the light emitting section  53  is positioned at the position of the light emitting section  52 . More specifically, in  FIG. 3A , the center ( 53   b ) of the light emitting section  53  is positioned at point R 0 . 
   On the other hand, as shown in  FIG. 7C , respective centers of the light emitting sections  50  and  52  are apart from each other by the distance L 1  in the direction of Y, and by the distance L 2  in the direction Z, respectively. The distance between the points R 0  and R 1  corresponds to the distance L 1 . When the rotationally moving section  5  moves the distance L 2  in the direction of Z, the discharge tube  3  projecting from the rotationally moving section  5  is also moved by the distance L 2 , and as a result, the center of the light emitting section  53  is also moved by the distance L 2  in the direction of Z. More specifically, as shown in  FIG. 3B , the distance in the direction of Z between opposite ends P 0  and P 1  of the slide groove  7 , which is formed in inclination in the inner wall of the rotationally moving section  5 , is the distance L 2  in the direction of Z of the light emitting section  53 . The ends P 0  and P 1  may not the opposite ends of the slide groove  7  when conditions that the distance in the direction of Z is equal to or exceed the distance L 2  are satisfied. 
   In the above arrangement, the operation of moving the light emitting section  53  to a position suitable for high beam and low beam will be explained hereinbelow. First, a case in which the light emitting section  53  is positioned at a low beam position, that is, a case in which the center of the light emitting section  53  is positioned at point R 1  will be explained. In such a case, the rotationally moving section  5  is positioned at the most forward position relative to the direction of Z, that is, the pin  8  is positioned at the end P 1  in the slide groove  7 . As described above, the central axis Q 1  of the light emitting section  53  is disposed on the circumference C 1  of the rotationally moving section  5  a radius r apart from the rotational central axis Q 0  of the rotating body  10  so as to be decentered therefrom. Consequently, when the rotationally moving section  5  is rotated in the direction of R shown in  FIGS. 3A and 3B  by a rotation controller (not shown), the central axis Q 1  of the light emitting section  53  moves on the circumference C 1 . When the distance between points R 1  and R 0  on a position parallel to the direction of Y is set to become equal to the distance L 1 , the light emitting section  53  is moved in the direction of Y suitable for high beam emission when the rotationally moving section  5  rotates an angle θ. 
   When the rotationally moving section  5  rotates an angle θ, the pin  8  projecting from the rotating body  10  which is coaxial with the rotationally moving section  5  slides in the slide groove  7  from the end P 1 . Since the pin  8  projecting from the rotating body  10  does not move in the direction of Z, the rotationally moving section  5  is moved in the direction of −Z as the pin  8  slides in the slide groove  7  toward the end P 0 . When rotating a predetermined amount of rotation (angle θ), the rotationally moving section  5  is moved to the most backward position relative to the direction of Z, that is, the pin  8  is moved to the end P 0  in the slide groove  7 . When the distance in the direction of Z between the ends P 1  and P 0  is set to become equal to the distance L 2 , the center of the light emitting section  53  is moved by the distance L 2  in the direction of −Z. Consequently, the light emitting section  53  is moved in the direction of Z suitable for high beam emission. 
   Accordingly, the light emitting section  53  can be moved from the position suitable for low beam emission to the position suitable for high beam emission by spirally rotating the rotationally moving section  5  in such a way that the central axis Q 1  of the light emitting section  53  is decentered from the rotational central axis Q 0  of the rotationally moving section  5 . In other words, by eccentrically rotating the discharge tube  3  while moving it forward and backward by the motor  9 , the light emitting section  53  thereof can be moved to an arbitrary position in three dimension, thereby being moved to the position in the reflecting mirror, which is suitable for low beam or high beam. 
   On the other hand, when the light emitting section  53  is moved from the position suitable for high beam emission to the position suitable for low beam emission, the light emitting section  53  can be moved as in the above by rotating the rotationally moving section  5  in the direction of L opposite to the above. More specifically, the light emitting section  53  is rotated from point R 0  (the end P 0 ) in the direction of L to move the rotationally moving section  5  forwardly (in the direction of +Z). The rotational quantum may be controlled by adjusting, for example, rotation time as well as the rotation angle. 
   An embodiment of the rotation controller for controlling the rotation of the rotationally moving section  5  will be described with reference to  FIGS. 4A and 4B , and FIG.  5 .  FIGS. 4A and 4B  show electrical connections for supplying power to the conventional headlamp, for explaining the operation of the rotation controller,  FIG. 4A  showing a positive control system and  FIG. 4B  showing a negative control system.  FIG. 5  shows a schematic circuit diagram of an embodiment of a rotation controller CC and connections with its peripheral devices. 
   In the positive control system shown in  FIG. 4A , one terminal of each of the high-beam and low-beam light emitting sections  52  and  50  of the halogen lamp  2  is connected to a common terminal C of a connecter (not shown), thereby being connected to an earth terminal of the vehicle. The other terminals of the light emitting sections  52  and  50  are connected to terminals L and H of a connector (not shown), respectively. The terminals L and H carry a voltage of 12V through switches S 1  and S 2 , respectively. In the negative control system shown in  FIG. 4B , one terminal of each of the high-beam and low-beam light emitting sections  52  and  50  of the halogen lamp  2  is connected to a common terminal C of a connecter (not shown), and carries a voltage of 12V. The other terminals of the light emitting sections  52  and  50  are connected to terminals L and H of a connector (not shown), respectively. The terminals L and H are each connected to an earth terminal of the vehicle through switches S 1  and S 2 , respectively. 
   In either of the positive control system and negative control system, upon closing the switch S 1 , voltage is applied to the low-beam light emitting section  50 , and low beam light is radiated. Upon closing the switch S 2 , voltage is applied to the high-beam light emitting section  52 , and high beam light is radiated. The positive control system and the negative control system are adopted depending on the type of vehicles. It is more economical that the rotation controller can be used in both control methods, which decreases vehicle assembly steps. 
   Referring to  FIG. 5 , the rotation controller CC can be used in both of the positive control system and negative control system and includes the following components: a drive unit  18  for switching the rotating direction of the rotation axis which rotates eccentrically, a timer circuit  17  for controlling the rotation time for the rotation axis, and switching circuits  16   a  and  16   b  for switching the polarity of a signal applied to the rotation controller CC. The switching circuits  16   a  and  16   b  are diode-bridge rectifying circuits composed of diodes D 1  to D 4  and D 5  to D 8 , respectively, the terminals a, c and g, and e are connected to terminals H 0 , C 0  and L 0  of a connector  15 , respectively. 
   Respective terminals b and f of the switching circuits  16   a  and  16   b  are connected to input terminals j and i of the timer circuit  17  and input terminals l and m of the drive unit  18 , respectively, and are connected to respective anode terminals of diodes D 9  and D 10 . Respective cathode terminals of the diodes D 9  and D 10  are connected to one terminal  3   a  of a relay-contact driving coil  30  for switching a relay contact connected to a power source for lighting up a discharge tube (not shown). Furthermore, a terminal d which is the node of anodes of diodes D 3  and D 4  of the switching circuit  16   a  and a terminal h which is the node of anodes of diodes D 7  and D 8  of the switching circuit  16   b  are connected to input terminals r and s of the drive unit  18 , respectively. The terminals d and h are connected to cathode terminals of diodes D 12  and D 11 , respectively. Anode terminals of the diodes D 12  and D 11  are each connected to an earth terminal p of the drive unit  18  and also connected to the other terminal  3   b  of the relay-contact driving coil  30 . Output terminals n and o of the drive unit  18  are each connected to the motor  9 . 
   An output terminal k of the timer circuit  17  is connected to an input terminal q of the drive unit  18 . Power-supply voltage (not shown) is applied to the timer circuit  17  and the drive unit  18 . The timer circuit  17  is a well-known Schmitt trigger circuit which is activated on the basis of time determined by a time constant of, for example, a resister and a capacitor, and the drive unit  18  is a well-known full-bridge circuit, which perform the following predetermined operations. To the input terminals i and j of the timer circuit  17 , signals for activating the timer circuit  17  are applied. Input terminals l and m of the drive unit  18  are terminals where signals for determining the rotating direction of the motor  9  are applied. The signals are applied to the input terminals of the well-known full-bridge circuit. 
     FIG. 5  also shows the connections with the respective switches S 1  and S 2  of the positive control system and the negative control system, shown in  FIGS. 4A and 4B , and the relay-contact driving coil  30 . The terminals H and L of the connector  15  are connected to one terminal of each switch S 2  and S 1 , respectively. The other terminals of the switches S 2  and S 1  are connected to a terminal F 1 , and a terminal C of the connector  15  is connected to a terminal F 2 . In the positive control system, the terminal F 1  is connected to a 12V power source and the terminal F 2  is grounded. In the negative control system, the terminal F 1  is grounded and the terminal F 2  is connected to the 12V power source. 
   The discharge tube  3  is connected from the respective output terminals b and f of the switching circuits  16   a  and  16   b  to one terminal  3   a  of the relay-contact driving coil  30  via the diodes D 9  and D 10 , and from the respective output terminals d and h of the switching circuits  16   a  and  16   b  to the other terminal  3   b  of the relay-contact driving coil  30  so that it lights up even when the switches S 1  and S 2  are closed in both of the positive control system and negative control system. Also, the relay-contact driving coil  30  may be connected in other ways; for example, the terminals H and L and the terminal C of the connector  15  may be connected to one terminal  3   a  of the relay-contact driving coil  30  and the other terminal  3   b , respectively. In such a case, even when either of the switches S 1  and S 2  is closed, the connection is established so that the voltage of the terminals H and L of the connector  15  is applied to the first terminal  3   a  of the relay-contact driving coil  30 . 
   As described above, the positive control system and negative control system have different polarities of voltage applied to the connector  15 . In the positive control system, as shown in  FIG. 4A , the terminal C is grounded and a voltage of +12V is applied to the terminals H and L via the switches S 2  and S 1 , respectively. In the negative control system, as shown in  FIG. 4B , a voltage of +12V is applied to the terminal C and the terminals H and L are grounded via the switches S 2  and S 1 , respectively. 
   In the positive control system, the terminal F 1  is impressed with +12V voltage and the terminal F 2  is grounded. In such a case, for example, when the switch S 2  is closed, the light emitting section  53  of the discharge tube  3 , shown in  FIG. 1 , is moved to the position for high beam emission as follows: When the switch S 2  is closed to apply +12V voltage to the terminal H and ground the terminal C, the switching circuit  16   a  is brought into conduction, so that the +12V voltage is applied to respective input terminals j and l of the timer circuit  17  and the drive unit  18 , and the earth terminal p is grounded. When +12V voltage is applied to the input terminal j of the timer circuit  17 , the timer circuit  17  outputs a signal to the output terminal k during a predetermined period of time and the motor  9  is rotated in a predetermined direction (the direction in which the rotationally moving section  5  rotates in the direction of R in  FIGS. 3A and 3B ) for the predetermined period of time (time that it rotates an angle θ in  FIGS. 3A and 3B ) by the drive unit  18  under the signal. 
   When the switch S 1  is closed, the light emitting section  53  of the discharge tube  3  is moved to a low-beam position as follows: When the switch S 1  is closed to apply +12V voltage to the terminal L and ground the terminal C, the switching circuit  16   b  is brought into conduction, so that the +12V voltage is applied to respective input terminals i and m of the timer circuit  17  and the drive unit  18 , and the earth terminal p is grounded. When the +12V voltage is applied to the input terminal i of the timer circuit  17 , the timer circuit  17  outputs a signal to the output terminal k during a predetermined period of time, so that the motor  9  is rotated in a predetermined direction (the direction in which the rotationally moving section  5  rotates in the direction of L in  FIGS. 3A and 3B ) for the predetermined period of time (time that it rotates an angle θ in  FIGS. 3A and 3B ) by the drive unit  18  under the signal. 
   In the negative control system, the terminal F 1  is grounded and the terminal F 2  is impressed with +12V voltage. In such a case, for example, when the switch S 2  is closed, the light emitting section  53  of the discharge tube  3  is moved to the position for high beam emission as follows: When the switch S 2  is closed to apply +12V voltage to the terminal C and ground the terminal H, the switching circuit  16   a  is brought into conduction, so that the +12V voltage is applied to respective input terminals j and l of the timer circuit  17  and the drive unit  18 , and the earth terminal p is grounded. When +12V voltage is applied to the input terminal j of the timer circuit  17 , the timer circuit  17  outputs a signal to the output terminal k during a predetermined period of time, so that the motor  9  is rotated in a predetermined direction (the direction in which the rotationally moving section  5  rotates in the direction of R in  FIGS. 3A and 3B ) for the predetermined period of time (time that it rotates an angle θ in  FIGS. 3A and 3B ) by the drive unit  18  under the signal. 
   When the switch S 1  is closed, the light emitting section  53  of the discharge tube  3  is moved to a low-beam position as follows: When the switch S 1  is closed to apply +12V voltage to the terminal C and ground the terminal L, the switching circuit  16   b  is brought into conduction, so that the +12V voltage is applied to respective input terminals i and m of the timer circuit  17  and the drive unit  18  and the earth terminal p is grounded. When the +12V voltage is applied to the input terminal i of the timer circuit  17 , the timer circuit  17  outputs a signal to the output terminal k during a predetermined period of time, so that the motor  9  is rotated in a predetermined direction (the direction in which the rotationally moving section  5  rotates in the direction of L in  FIGS. 3A and 3B ) for the predetermined time (time that it rotates an angle θ in  FIGS. 3A and 3B ) by the drive unit  18  under the signal. 
   Switching circuits (not shown), which use a transistor for example, are connected in series to the input terminals l and m of the drive unit  18 , respectively, and operate as will be described later so that even when the +12V voltage is applied to the input terminals l and m of the drive unit  18  simultaneously in the negative control system, the voltage applied to any one of the input terminals become effective. In other words, in the negative control system, the terminal F 1  is grounded and the terminal F 2  is impressed with the +12V voltage. For example, when the switch S 2  is closed to apply +12V voltage to the terminal C and ground the terminal H, the diode D 2  of the switching circuit  16   a  is brought into conduction, the input terminals j and l are each impressed with the +12V voltage, the earth terminal p is grounded, and also the diode D 6  of the switching circuit  16   b  is brought into conduction to apply the +12V voltage to the input terminal m of the drive unit  18 . Accordingly, in this state, unless the voltage applied to the input terminal m is made ineffective and the voltage applied to the input terminal l is made effective, a problem occurs in that the motor  9  cannot be rotated in a predetermined direction. The same can be said for the case in which the switch S 1  is closed. Unless the voltage applied to the input terminal l is made ineffective and the voltage applied to the input terminal m is made effective, a problem occurs in that the motor  9  cannot be rotated in a predetermined direction. 
   In order to solve the above problems, the voltage that is applied to signal lines each connected to input terminals r and s of the drive unit  18  from the respective terminals d and h of the switching circuits  16   a  and  16   b  is applied as control signals for the switching circuits (not shown) to activate the switching circuits as follows: When the switch S 2  is closed to apply +12V voltage to the terminal C and ground the terminal H, the terminal L is opened. As a result, the input terminal r of the drive unit  18  is grounded via the diode D 4 , but a cathode terminal of the diode D 8  is opened and the input terminal s of the drive unit  18  connected to an anode terminal of the diode D 8  is opened. The switching circuits (not shown) provided for the drive unit  18  are closed when the input terminal r or s of the drive unit  18  is grounded, and are opened when it is opened. Accordingly, only the signal voltage applied to the input terminal l of the drive unit  18  becomes effective to rotate the motor  9  in a predetermined direction. 
   The similar goes on when the switch S 1  is closed and +12V voltage is applied to the terminal C and the terminal L is grounded. Specifically, when the switch S 1  is closed to apply +12V voltage to the terminal C and ground the terminal L, the terminal H is opened. Consequently, the input terminal s of the drive unit  18  is grounded via the diode D 8 ; however, a cathode terminal of the diode D 4  is opened and the input terminal r of the drive unit  18  that is connected to an anode terminal of the diode D 4  is opened. The switching circuits (not shown) provided for the drive unit  18  are closed when the input terminal r or s of the drive unit  18  is grounded, and are opened when it is opened. Accordingly, only the signal voltage applied to the input terminal m of the drive unit  18  becomes effective to rotate the motor  9  in a predetermined direction. 
   As described above, the switching circuits (not shown) connected in series to the respective input terminals l and m of the drive unit  18  make only one of the input terminals l and m of the drive unit  18  effective, even in the negative control system, to allow the motor  9  to rotate in a predetermined direction. 
   The operation of the discharge tube control section A, which is activated by the rotation controller CC, will be described hereinbelow, returning to FIG.  1 . In either the positive control system or negative control system, when either of the switches S 1  and S 2  is closed, the motor  9  rotates in a predetermined direction for a predetermined period of time. The gear  11  fitted to the rotation axis of the motor  9  is rotated with the rotation of the motor  9 . The rotation of the motor  9  is decreased in speed through the gears  11 ,  14  and  12  and transmitted to the gear  13 . The rotating body  10 , which is fitted to and projects from the rotation axis (the central axis of the rotation is Q 1 ) of the gear  13 , is rotated with the rotation of the gear  13 . When the rotating body  10  rotates, the pin  8  projecting from the side thereof moves in the slide groove  7  formed in a slanting position in the inner wall of the rotationally moving section  5 . 
   Since the pin  8  projecting from the rotating body  10  does not move in the direction of Z, as the pin  8  slides in the slide groove  7 , the rotationally moving section  5  is moved in the direction of Z. The discharge tube  3  is secured to the rotationally moving section  5  and the axis of the light emitting section  53  of the discharge tube  3  and the axis of the rotationally moving section  5  are decentered from each other. Consequently, the light emitting section  53  moves spirally to positions in the directions of Y and Z, which are suitable for high-beam and low-beam emission. The discharge tube  3  of the discharge tube control section A is covered with the shade  51 , so that the light distribution of low beam and high beam of the discharge tube  3  can be switched by moving the light emitting section  53  to the above positions. 
   According to the present invention, there is provided a vehicle headlamp capable of switching light distribution of high beam and low beam by moving a light emitting section using a simple rotation mechanism. A light source having a single light emitting section, such as a discharge tube, and a reflecting mirror, as known in the art, can be used, thus remarkably improving the performance of a vehicle headlamp. 
   The vehicle headlamp according to the present invention can be used irrespective of whether the positive control system or the negative control system is adopted for supplying power to the vehicle headlamp, so that there is no need to use different parts depending on the type of vehicles. Consequently, it is economical and the vehicle assembly steps can be decreased.