Patent Publication Number: US-8523414-B2

Title: Vehicle headlamp

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a lighting device and more particularly to a vehicle headlamp which includes a reflector for reflecting a light emitted from a light source. 
     2. Related Art 
     There is a lighting device for a vehicle using a semiconductor light emitting device such as an LED (Light Emitting Diode). JP-A-2008-226707 discloses a lighting device for a vehicle in which a light emitted from each of LEDs is reflected by a reflector so as to form a light distribution pattern for a hot zone and a light distribution pattern for a diffusion region. 
     In order to enhance a distance visibility, it is important to increase a luminous intensity in a vicinity of an upper cut-off line in a light distribution pattern for a low beam, thereby causing the cut-off line to be clear. Some reflectors have a plurality of reflecting surfaces and synthesize lights (projection images) reflected by respective reflecting surfaces, thereby forming a light distribution pattern for a low beam which has the cut-off line. 
     Depending on a design of a vehicle, however, a shape of a lighting device for a vehicle is restricted. For example, it is considered, in a lighting device for a vehicle, to take away a part of a reflector. Each reflecting surface of the reflector forms a part of a light distribution pattern for a low beam. Therefore, it is hard to form a desirable light distribution pattern if a part of reflecting surfaces is decreased. If reflecting surfaces for forming a cut-off line of the light distribution pattern for a low beam are decreased, particularly, it is difficult to form a clear cut-off line. 
     SUMMARY OF THE INVENTION 
     One or more embodiments provide a vehicle headlamp which forms a desirable light distribution pattern. 
     According to one or more embodiments of the present invention, a vehicle headlamp comprises a light source having a light emitting surface, the light emitting surface including at least a linear side, and a reflector adapted to reflect light emitted by the light source to form a light distribution pattern having a first cut-off line and a second cut-off line. The first cut-off line and the second cut-off line intersect each other with an angle. The vehicle headlamp comprises an optical axis and a transverse direction of a vehicle, which is perpendicular to the optical axis. The reflector comprises a left region disposed on a left side in the transverse direction, and a right region disposed on a right side in the transverse direction. Areas of the right region and the left region are different from each other. The reflector further comprises a plurality of first reflecting portions configured to form the first cut-off line by images of said linear side of the light emitting surface reflected on the first reflecting portions and a plurality of second reflecting portions configured to form the second cut-off line by images of said linear side of the light emitting surface reflected on the second reflecting portions. The light source is disposed so that said linear side of the light emitting surface is oblique with respect to the optical axis and both of the first reflecting portions and the second reflecting portions are positioned in one of the right region and the left region having a larger area. 
     According to one or more embodiments of the present invention, the light source is disposed so that the light emitting surface is directed downward. 
     According to one or more embodiments of the present invention, a vehicle headlamp comprises a light source having a light emitting surface, the light emitting surface including at least a linear side, and a reflector adapted to reflect light emitted by the light source to form a light distribution pattern having a first cut-off line and a second cut-off line. The first cut-off line and the second cut-off line intersect each other with an angle. The reflector comprises an upper region disposed on an upper side and a lower region disposed on a lower side with respect to an optical axis. Areas of the upper region and the lower region are different from each other. The reflector further comprises a plurality of first reflecting portions configured to form the first cut-off line by images of said linear side of the light emitting surface reflected on the first reflecting portions and a plurality of second reflecting portions configured to form the second cut-off line by images of said linear side of the light emitting surface reflected on the second reflecting portions. The light source is disposed so that said linear side of the light emitting surface is oblique with respect to the optical axis and both of the first reflecting portions and the second reflecting portions are positioned in one of the upper region and the lower region having a larger area. 
     According to one or more embodiments of the present invention, the light source is disposed so that the light emitting surface is directed in a transverse direction of a vehicle, which is perpendicular to the optical axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(   a ) is a front view showing a vehicle headlamp according to a first embodiment.  FIG. 1(   b ) is a P-P sectional view of  FIG. 1(   a ). 
         FIG. 2  is a view showing a light emitting module seen from a visual point R in  FIG. 1 . 
         FIGS. 3(   a ) to  3 ( d ) are views showing a shape of a reflector. 
         FIG. 4  is a view showing a light distribution pattern PL for a low beam which is formed on a virtual vertical screen by a lighting unit. 
         FIG. 5(   a ) is a view schematically showing each segment included in a hot zone forming portion.  FIG. 5(   b ) is a view showing a light distribution pattern PA for a hot zone which is formed on the virtual vertical screen by the hot zone forming portion. 
         FIG. 6(   a ) is a view schematically showing each segment included in a diffusion region forming portion.  FIG. 6(   b ) is a view showing a first diffusion light distribution pattern PB 1  formed on the virtual vertical screen by the diffusion region forming portion. 
         FIG. 7(   a ) is a view schematically showing each segment included in the diffusion region forming portion.  FIG. 7(   b ) is a view showing a second diffusion light distribution pattern PB 2  formed on the virtual vertical screen by the diffusion region forming portion. 
         FIG. 8  is a front view showing a reflector, a part of which is taken away. 
         FIG. 9(   a ) is a front view schematically showing a reflector according to the first embodiment.  FIG. 9(   b ) is a top view showing a tilt of a light source according to the first embodiment.  FIG. 9(   c ) is a view showing a line connecting reflecting portions for forming a first cut-off line and a line connecting reflecting portions for forming a second cut-off line in the reflector of  FIG. 9(   a ).  FIG. 9(   d ) is a view showing an angle of a projection image in reflecting portions E to H of the reflector in  FIG. 9(   a ). 
         FIG. 10(   a ) is a front view schematically showing a reflector according to a second embodiment.  FIG. 10(   b ) is a top view schematically showing the reflector according to the second embodiment.  FIG. 10(   c ) is a perspective view schematically showing the reflector according to the second embodiment.  FIG. 10(   d ) is a side view showing a tilt of a light source according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be described below in detail with reference to the drawings. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. It is assumed that the same or equivalent components, members, and processings shown in the respective drawings have the same reference numerals, and repetitive description will be properly omitted. The embodiments described herein are not intended to limit the invention but only as examples of the invention, and all features or combinations of the features of the embodiments are not always essential to the invention. 
     (First Embodiment) 
     First of all, a basic structure of a vehicle headlamp according to one or more embodiments of the invention will be described. 
       FIG. 1(   a ) is a front view showing a headlamp  10  for a vehicle according to a first embodiment, and  FIG. 1(   b ) is a P-P sectional view in  FIG. 1(   a ). The headlamp  10  for a vehicle has a housing  12 , an outer cover  14  and a lighting unit  16 . Description will be given on the assumption that a direction of an arrow X indicates a forward part of a lighting device in  FIG. 1(   b ). Moreover, right and left sides seen from the forward part of the lighting device will be referred to as right and left sides of the lighting device, respectively. The headlamp  10  for a vehicle is provided in each of left and right front parts of the vehicle.  FIGS. 1(   a ) and  1 ( b ) show a structure of the headlamp  10  for a vehicle on the left or right part. 
     The housing  12  is formed to take a shape of a box which has an opening. The outer cover  14  is formed to take a shape of a bowl by a resin or a glass having translucency. The outer cover  14  has an edge part attached to the opening portion of the housing  12 . Thus, a lamp housing is formed in a region covered with the housing  12  and the outer cover  14 . 
     The lighting unit  16  is provided in the lamp housing. The lighting unit  16  is disposed in the lamp housing to irradiate a light on the forward part of the lighting device. The lighting unit  16  has a support plate  18 , a support member  20 , a light emitting module  22 , a reflector  24 , a shade  26 , a heat sink  28 , and a cooling fan  30 . The lighting unit  16  is used as a light source for a low beam which forms a light distribution pattern for a low beam to be irradiated onto the forward part of the vehicle. An extension reflector  34  is provided in the forward part of the lighting device in the lighting unit  16 . The extension reflector  34  has an opening portion for causing a light reflected by the reflector  24  to advance to the forward part of the lighting device. 
     The support plate  18  is fixed to the housing  12  with an aiming screw  32  in three places of a corner portion. The support member  20  is formed to take a shape of a thick rectangular plate, and one of side surfaces is fixed to a front surface of the support plate  18 . The light emitting module  22  to be a light source is attached to a lower surface of the support member  20  in such a manner that a main optical axis is turned slightly rearward from the lighting device. The support member  20  is formed by a material having a high heat conductivity, such as aluminum, in order to enable an efficient collection of a heat emitted from the light emitting module  22 . The cooling fan  30  is attached to an upper surface of the support member  20  through the heat sink  28 . Thus, the light emitting module  22  is cooled by the cooling fan  30  through the support member  20  and the heat sink  28  so that a rise in a temperature is suppressed. 
     The reflector  24  is attached to the front surface of the support plate  18  so as to be positioned under the support member  20 . The reflector  24  functions as an optical member for collecting the light emitted from the light emitting module  22  toward the front part of the lighting device. More specifically, the reflector  24  reflects the light emitted from the light emitting module  22  toward the front part of the lighting device, thereby forming a light distribution pattern for a low beam. 
     The shade  26  is formed like a plate and is disposed almost vertically in the vicinity of the light emitting module  22 . The shade  26  shields any lights reflected forward from the lighting device by the reflector  24 , which is reflected by the extension reflector  34  and is turned upward from the light distribution pattern for a low beam. In other words, the shade  26  shields at least a part of the light turned toward the extension reflector  34  which is not an effective reflecting surface. Consequently, it is possible to suppress a glare to be given to a person present in the forward part of the vehicle through the light reflected by the extension reflector  34  which is a non-effective reflecting surface. The shade  26  does not need to be disposed vertically and may be provided horizontally or with a tilt to a horizontal direction. Moreover, the shade  26  is disposed in a position in which a light turned directly from the light emitting module  22  toward the reflector  24  is not shielded. 
       FIG. 2  is a view showing the light emitting module  22  seen from the visual point R of  FIG. 1 . The light emitting module  22  has a light emitting device line  52  constituted by a plurality of light emitting devices  50  and a substrate  54 . In the first embodiment, four light emitting devices  50  are provided. The four light emitting devices  50  are mounted on the substrate  54 . It is a matter of course that the number of the light emitting devices  50  is not restricted to four, and at least one light emitting device  50  or more may be provided. 
     The light emitting device  50  has a semiconductor light emitting device (not shown) and a phosphor (not shown). In the first embodiment, the light emitting device  50  is provided to emit a white light. More specifically, a blue LED for mainly emitting a blue light is employed for the semiconductor light emitting device. Moreover, there is employed a phosphor for carrying out a wavelength conversion from a blue light to an yellow light. When the semiconductor light emitting device emits a light, additive color mixing is carried out over the blue light emitted from the semiconductor light emitting device and the yellow light subjected to the wavelength conversion by the phosphor so that a white light is emitted from a light emitting plane of the light emitting device  50 . Thus, the semiconductor light emitting device and the phosphor are well-known. For this reason, detailed description will be omitted. 
     It is a matter of course that the light emitting device  50  is not restricted to the emission of the white light, and may emit lights having other colors, for example, a light yellow color, a light blue color, and the like. Moreover, the semiconductor light emitting device may mainly emit a light having a wavelength other than a blue color, for example, ultraviolet rays. 
     In the first embodiment, each of the light emitting devices  50  is formed to take a square shape. Each of the light emitting devices  50  may be formed to take a rectangular shape other than the square shape. Each of the light emitting devices  50  may be arranged in a line in a state in which one of edges is provided in contact with one of edges of the adjacent light emitting device  50  to constitute a light emitting device line  52 . Accordingly, the light emitting device line  52  functions as an integral surface light source having a slender and rectangular light emitting surface  52   a . In place of the light emitting device line  52 , a slender and rectangular light emitting device may be singly used. Moreover, the light emitting surface  52   a  of the light emitting device line  52  may be formed to take a shape other than the rectangular shape. Furthermore, the light emitting surface  52   a  does not need to be a flat surface but it is sufficient that the light emitting surface  52   a  has edges for forming a first cut-off line CL 1  and a second cut-off line CL 2  as will be described below. 
     The light emitting surface  52   a  is formed to be a slender rectangle. For this reason, the light emitting surface  52   a  has four edges in total, that is, two long linear edges and two short linear edges. An upper edge  52   b  to be a long one of the four edges is utilized for forming a cut-off line having a light distribution pattern for a low beam. 
       FIGS. 3(   a ) to  3 ( d ) are views showing a shape of the reflector  24 . More specifically,  FIGS. 3(   a ),  3 ( b ) and  3 ( c ) are perspective, front and top views showing the reflector  24 , respectively.  FIG. 3(   d ) is a Q-Q sectional view in  FIG. 3(   c ). 
     The reflector  24  has a reflecting surface  24   a  and a concave portion  24   b . The concave portion  24   b  is formed to take an almost identical shape to an external shape below the support member  20 . The concave portion  24   b  is fitted into a lower part of the support member  20  so that the reflector  24  is positioned with respect to the support member  20 . 
     The reflecting surface  24   a  has a hot zone forming portion  24 A and diffusion region forming portions  24 B and  24 C. The hot zone forming portion  24 A is disposed between the diffusion region forming portions  24 B and  24 C. The diffusion region forming portion  24 B is disposed on a right side of the hot zone forming portion  24 A with the reflector  24  seen from a front, that is, toward a rear part of the lighting device, and the diffusion region forming portion  24 C is disposed on a left side of the hot zone forming portion  24 A toward a rear part of the lighting device. The hot zone forming portion  24 A reflects the light emitted from the light emitting module  22  toward the front part of the lighting device, thereby forming a light distribution pattern for a hot zone which will be described below. The diffusion region forming portions  24 B and  24 C reflect the light emitted from the light emitting module  22  toward the forward part of the lighting device, thereby forming a diffusion light distribution pattern which will be described below. 
     The hot zone forming portion  24 A is disposed in such a manner that an average distance to the light emitting module  22  is shorter than that of each of the diffusion region forming portions  24 B and  24 C. The average distance indicates an average value of a distance between a surface of each of the hot zone forming portion  24 A and the diffusion region forming portions  24 B and  24 C and a center of the light emitting module  22 , and may be calculated by an integration. Consequently, it is possible to simply form a hot zone having a high illuminance. 
     Each of the hot zone forming portion  24 A and the diffusion region forming portions  24 B and  24 C has a plurality of segments. Each of the segments is formed as a smooth curved surface and is connected to an adjacent segment provided in contact with each other at edges through a step or a fold. 
       FIG. 4  is a view showing a light distribution pattern PL for a low beam which is formed on the virtual vertical screen by the lighting unit  16 . The light distribution pattern PL for a low beam has the first cut-off line CL 1  and the second cut-off line CL 2  which are extended in non-parallel and intersect with each other at an angle. The first cut-off line CL 1  is extended in a horizontal direction slightly downward (0.6 degree) from a horizontal line (an H-H line) at a right side of a vertical line (a V-V line) extended in a vertical direction from a vanishing point. The second cut-off line CL 2  is extended with a tilt so as to be gradually higher in a leftward direction from an intersecting point of the first cut-off line CL 1  and the V-V line. The shade  26  is provided to shield an upward light from the first cut-off line and the second cutoff line. 
     The lighting unit  16  forms the light distribution pattern PL for a low beam. More specifically, the hot zone forming portion  24 A reflects the light emitted from the light emitting module  22  and thus forms a light distribution pattern PA for a hot zone which includes the first cut-off line and the second cut-off line. The diffusion region forming portions  24 B and  24 C form a diffusion light distribution pattern PB which is longer in the horizontal direction than the light distribution pattern PA for a hot zone. As described above, the hot zone forming portion  24 A is disposed between the diffusion region forming portions  24 B and  24 C. Thus, the diffusion region forming portions  24 B and  24 C for diffusing a light are disposed on an outside of the hot zone forming portion  24 A. Consequently, it is possible to avoid requiring a complicated shape of the reflector  24 . 
     The light distribution pattern PL for a low beam is formed by causing the light distribution pattern PA for a hot zone and the diffusion light distribution pattern PB to overlap with each other. The diffusion light distribution pattern PB is formed to be extended in the horizontal direction and has a length in the horizontal direction which is the same as the light distribution pattern PL for a low beam. The diffusion light distribution pattern PB forms the first cut-off line CL 1  by an upper edge on the right side of the V-V line. 
     The light distribution pattern PA for a hot zone is formed to include a hot zone having an illuminance to be increased in the light distribution pattern PL for a low beam. The light distribution pattern PA for a hot zone includes the first cut-off line CL 1  and the second cut-off line CL 2  which intersect with each other at an angle. The light distribution pattern PA for a hot zone is formed in such a manner that lengths in both a horizontal direction and a vertical direction are smaller than the diffusion light distribution pattern PB. 
       FIG. 5(   a ) is a view schematically showing each segment included in the hot zone forming portion  24 A and  FIG. 5(   b ) is a view showing the light distribution pattern PA for a hot zone which is formed on the virtual vertical screen by the hot zone forming portion  24 A.  FIG. 5(   a ) is a view showing the reflector  24  seen from a front, that is, a view showing the reflector  24  seen toward the rear part of the lighting device.  FIG. 5(   b ) is a view showing the light distribution pattern PA for a hot zone which is formed on the virtual vertical screen by the hot zone forming portion  24 A as seen toward the front part of the lighting device. 
     The hot zone forming portion  24 A has six segments A 1  to A 6  which are formed by a division into three lines in a vertical direction and two lines in a transverse direction. Each of the segments A 1  to A 6  is formed to take a rectangular shape. The segments A 1  to A 3  are included in a left line toward the rear part of the lighting device and are disposed in order of the segments A 1 , A 2  and A 3  from a top toward a bottom. The segments A 4  to A 6  are included in a right line toward the rear part of the lighting device and are disposed in order of A 4 , A 5  and A 6  from the top toward the bottom. 
     The light distribution pattern PA for a hot zone is formed by a superposition of projection images PA 1  to PA 6 . Each of the projection images PA 1  to PA 6  is formed through a light reflected by each of the segments A 1  to A 6 . 
     Each of the segments A 1  to A 3  forms the projection images PA 1  to PA 3  extended in the horizontal direction by utilizing the fact that the light emitting surface  52   a  is formed to take a slender and rectangular shape. More specifically, the projection image PA 1  has a length in the horizontal direction which is almost equal to that of the light distribution pattern PA for a hot zone. The projection image PA 1  is formed in such a manner that an upper edge overlaps with the first cut-off line CL 1 . Moreover, the projection image PA 1  is formed in such a manner that a central part in the horizontal direction is positioned on a right side of the V-V line. 
     The projection image PA 2  has a length in the horizontal direction which is smaller than the projection image PA 1  The projection image PA 2  is also formed in such a manner that an upper edge overlaps with the first cut-off line CL 1  and a central part in the horizontal direction is positioned on a slightly right side of the V-V line. The projection image PA 3  has a length in the horizontal direction which is smaller than the projection image PA 2 . The projection image PA 3  is formed in such a manner that an upper edge overlaps with the first cut-off line CL 1  and a central part in the horizontal direction is positioned on the slightly right side of the V-V line. 
     Thus, the segments A 1  to A 3  form a light distribution pattern in which the projection images PA 1  to PA 3  are superposed, and are thus extended in the horizontal direction in such a manner that the upper edges overlap with the first cut-off line CL 1 , and furthermore, form a light distribution pattern in which an illuminance is gradually increased closer to the vanishing point. 
     The respective segments A 4  to A 6  form the projection images PA 4  to PA 6  extended in almost parallel with the second cut-off line CL 2  by utilizing the fact that the light emitting surface  52   a  is formed to take a slender and rectangular shape. More specifically, the projection image PA 4  is formed with an oblique extension in such a manner that the upper edge overlaps with a full length of the second cut-off line CL 2 . For this reason, the projection image PA 4  has an almost half length of the light distribution pattern PA for a hot zone. Moreover, the projection image PA 4  is formed in such a manner that a right end is positioned on a slightly right side from the V-V line and a left end is positioned on a left end of the light distribution pattern PA for a hot zone. 
     The projection image PA 5  is formed in such a manner that both lengths in directions which are parallel with the second cut-off line CL 2  and are perpendicular thereto are smaller than the length of the projection image PA 4 . The projection image PA 5  is also formed with an oblique extension in such a manner that an upper edge overlaps with the second cutoff line CL 2 . Moreover, the projection image PAS is formed in such a manner that a right end is positioned between the vanishing point and the right end of the projection image PA 4  and a left end is positioned closer to the vanishing point than the left end of the projection image PA 4 . 
     The projection image PA 6  is formed in such a manner that both lengths in the directions which are parallel with the second cut-off line CL 2  and are perpendicular thereto are smaller than the length of the projection image PAS. The projection image PA 6  is also formed with an oblique extension in such a manner that an upper edge overlaps with the second cutoff line CL 2 . Moreover, the projection image PA 6  is formed in such a manner that a right end is positioned between the vanishing point and the right end of the projection image PAS and a left end is positioned closer to the vanishing point than the left end of the projection image PAS. 
     Thus, the segments A 4  to A 6  form a light distribution pattern in which the projection images PA 4  to PA 6  are superposed, and are thus extended obliquely in such a manner that the upper edges overlap with the second cut-off line CL 2 , and furthermore, form a light distribution pattern in which an illuminance is gradually increased closer to the vanishing point. 
     The hot zone forming portion  24 A forms the first cut-off line CL 1  and the second cut-off line CL 2  through an image reflected by the same upper edge  52   b  of the light emitting surface  52   a . In recent years, a development of a surface emitting source having a light emitting surface over a plane, for example, an LED light source is rapidly advanced. The surface emitting source has an edge. By utilizing the edge of the surface emitting source to form a cut-off line, it is possible to simply form a clear cut-off line. 
     In the first embodiment, furthermore, the light emitting device line  52  having the slender and rectangular light emitting surface  52   a  is utilized as a light source. Therefore, the light emitted from the light emitting surface can be prevented from being excessively diffused and reflected in order to form a slender light distribution pattern. Thus, it is possible to form a clear cut-off line more easily. 
     Furthermore, the segments A 1  to A 3  form the first cut-off line CL 1  with an image reflected by the upper edge  52   b  in the light emitting surface  52   a . The segments A 4  to A 6  form the second cut-off line with an image reflected by the upper edge  52   b  in the light emitting surface  52   a . Thus, the first cut-off line CL 1  and the second cut-off line CL 2 , which are extended at an angle with respect to each other, are formed with the image reflected by the same upper edge  52   b  of the light emitting surface  52   a . Consequently, it is possible to reduce a cost required for the light emitting device more greatly as compared with the case in which the first cut-off line CL 1  and the second cut-off line CL 2  are formed with an image reflected by the two light emitting device lines  52  which are extended at an angle with respect to each other, for example. 
     Moreover, the segments A 1  to A 3  forming the first cut-off line CL 1  and the segments A 4  to AG forming the second cut-off line CL 2  are disposed adjacently to each other. Consequently, it is possible to reduce a size of the hot zone forming portion  24 A more greatly as compared with the case in which the segments A 1  to A 3  and the segments A 4  to A 6  are separated from each other, for example. 
     It is sufficient that any of the segments A 1  to A 3  forms the first cut-off line CL 1  and the residues do not need to form the first cut-off line CL 1 . Moreover, it is sufficient that any of the segments A 4  to A 6  forms the second cut-off line CL 2  and the residues do not need to form the second cut-off line CL 2 . 
       FIG. 6(   a ) is a view schematically showing each segment included in the diffusion region forming portion  24 B, and  FIG. 6(   b ) is a view showing a first diffusion light distribution pattern PB 1  formed on the virtual vertical screen through the diffusion region forming portion  24 B.  FIG. 6(   a ) is a view showing the reflector  24  seen from a front, that is, the reflector  24  seen toward the rear part of the lighting device.  FIG. 6(   b ) is a view showing the first diffusion light distribution pattern PB 1  formed on the virtual vertical screen through a light reflected by the diffusion region forming portion  24 B toward the front part of the lighting device. 
     The diffusion region forming portion  24 B is divided into two lines in a vertical direction. An upper one of the lines is divided into two segments arranged in a transverse direction and a lower one of the lines is divided into three segments arranged in the transverse direction. As a result, the diffusion region forming portion  24 B is divided into five segments B 1  to B 5 . Each of the segments B 1  and B 2  is formed to take a rectangular shape. A lower edge of the diffusion region forming portion  24 B takes a shape of a circular arc. Therefore, each of the segments B 3  to B 5  is formed to take a trapezoidal shape in which a rectangular lower part is obliquely cut out. The segments B 1  and B 2  are disposed in order of the segments B 1  and B 2  from left to right toward the rear part of the lighting device in the upper line of the diffusion region forming portion  24 B. The segments B 3  to B 5  are disposed in order of the segments B 3  to B 5  from left to right toward the rear part of the lighting device in the lower line of the diffusion region forming portion  24 B. 
     The first diffusion light distribution pattern PB 1  is formed by a superposition of the projection images PB 11  to PB 15 . Each of the projection images PB 11  to PB 15  is formed with a light reflected by each of the segments B 1  to B 5 . 
     The respective segments B 1  to B 5  form the projection images PB 11  to PB 15  extended in the horizontal direction by utilizing the fact that the light emitting surface  52   a  is formed to take a slender and rectangular shape. More specifically, the projection image PB 11  is formed to be extended in the horizontal direction in a smaller length than the diffusion light distribution pattern PB. At this time, the projection image PB 11  is formed in such a manner that a right end is positioned on the right end of the diffusion light distribution pattern PB toward the front part of the lighting device and a left end is positioned closer to the V-V line than the left end of the diffusion light distribution pattern PB. Moreover, the projection image PB 11  is formed in such a manner that an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 12  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 11 . At this time, the projection image PB 12  is formed in such a manner that a right end is positioned on the right end of the diffusion light distribution pattern PB toward the front part of the lighting device and a left end is positioned closer to the V-V line than the left end of the projection image PB 11 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 13  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 12 . At this time, the projection image PB 13  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line, a left end is positioned closer to the V-V line than the left end of the projection image PB 12 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 14  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 13 . At this time, the projection image PB 14  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line, left and right ends are positioned closer to the V-V line than the left and right ends of the projection image PB 13 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 15  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 14 . At this time, the projection image PB 15  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line, and left and right ends are positioned closer to the V-V line than the left and right ends of the projection image PB 14 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
       FIG. 7(   a ) is a view schematically showing each segment included in the diffusion region forming portion  24 C, and  FIG. 7(   b ) is a view showing a second diffusion light distribution pattern PB 2  formed on the virtual vertical screen through the diffusion region forming portion  24 C.  FIG. 7(   a ) is a view showing the reflector  24  seen from a front, that is, the reflector  24  seen toward the rear part of the lighting device.  FIG. 7(   b ) is a view showing the second diffusion light distribution pattern formed on the virtual vertical screen PB 2  through a light reflected by the diffusion region forming portion  24 C as seen toward the front part of the lighting device. 
     The diffusion region forming portion  24 C is divided into two lines in a vertical direction. An upper one of the lines is divided into two segments arranged in a transverse direction and a lower one of the lines is divided into three segments arranged in the transverse direction. As a result, the diffusion region forming portion  24 C is divided into five segments C 1  to C 5 . Each of the segments C 1  and C 2  is formed to take a rectangular shape. A lower edge of the diffusion region forming portion  24 C takes a shape of a circular arc. Therefore, each of the segments C 3  to C 5  is formed to take a trapezoidal shape in which a rectangular lower part is obliquely cut out. The segments C 1  and C 2  are disposed in order of the segments C 1  and C 2  from right to left toward the rear part of the lighting device in the upper line of the diffusion region forming portion  24 C. The segments C 3  to C 5  are disposed in order of the segments C 3  to C 5  from right to left toward the rear part of the lighting device in the lower line of the diffusion region forming portion  24 C. 
     The second diffusion light distribution pattern PB 2  is formed by a superposition of the projection images PB 21  to PB 25 . Each of the projection images PB 21  to PB 25  is formed with a light reflected by each of the segments C 1  to C 5 . 
     The respective segments C 1  to C 5  form the projection images PB 21  to PB 25  extended in the horizontal direction by utilizing the fact that the light emitting surface  52   a  is formed to take a slender and rectangular shape. More specifically, the projection image PB 21  is formed to be extended in the horizontal direction in a smaller length than the diffusion light distribution pattern PB. At this time, the projection image PB 21  is formed in such a manner that a left end is positioned on the left end of the diffusion light distribution pattern PB toward the front part of the lighting device and a right end is positioned closer to the V-V line than the right end of the diffusion light distribution pattern PB. Moreover, the projection image PB 21  is formed in such a manner that an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 22  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 21 . At this time, the projection image PB 22  is formed in such a manner that a left end is positioned on the left end of the diffusion light distribution pattern PB toward the front part of the lighting device and a right end is positioned closer to the V-V line than the right end of the projection image PB 21 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 23  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 22 . At this time, the projection image PB 23  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line and a right end is positioned closer to the V-V line than the right end of the projection image PB 22 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 24  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 23 . At this time, the projection image PB 24  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line and left and right ends are positioned closer to the V-V line than the left and right ends of the projection image PB 23 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     The projection image PB 25  is formed to be extended in the horizontal direction in a smaller length than the projection image PB 24 . At this time, the projection image PB 25  is formed in such a manner that a central part in the horizontal direction is positioned in the vicinity of the V-V line and left and right ends are positioned closer to the V-V line than the left and right ends of the projection image PB 24 , and furthermore, an upper edge overlaps with the first cut-off line CL 1 . 
     Thus, the diffusion region forming portion  24 B fot ns the first diffusion light distribution pattern PB 1  on which the projection images PB 11  to PB 15  are superposed through the segments B 1  to B 5 . Moreover, the diffusion region forming portion  24 C forms the second diffusion light distribution pattern PB 2  on which the projection images PB 21  to PB 25  are superposed through the segments C 1  to C 5 . Accordingly, the diffusion region forming portions  24 B and  24 C superpose the first diffusion light distribution pattern PB 1  and the second diffusion light distribution pattern PB 2 , thereby forming the diffusion light distribution pattern PB in which the upper edge is extended in the horizontal direction to overlap with the first cut-off line CL 1  and has an illuminance increased closer to the vanishing point. 
     In some cases in which the headlamp  10  for a vehicle is to be applied to the vehicle, it is hard to exactly mount the reflector  24  in respect of a design or a space. In those cases, the reflector takes such a shape that a part thereof is taken away, and an effective reflecting surface thereof is not symmetrical. 
       FIG. 8  is a front view showing a reflector, a part of which is taken away. In a reflector  60  shown in  FIG. 8 , a part of the hot zone forming portion  24 A is taken away. In other words, as compared with the reflector  24  shown in  FIG. 5 , the reflector  60  taking a symmetrical shape does not have a part of a reflecting surface forming a cut-off line. For this reason, a distance visibility is deteriorated in that state. As a result of earnest investigations, therefore, the inventor found the employment of the following structure. 
       FIG. 9(   a ) is a front view schematically showing a reflector according to a first embodiment,  FIG. 9(   b ) is a top view showing a tilt of a light source according to the first embodiment,  FIG. 9(   c ) is a view showing a line connecting reflecting portions for forming a first cut-off line and a line connecting reflecting portions for forming a second cut-off line in the reflector of  FIG. 9(   a ), and  FIG. 9(   d ) is a view showing an angle of a projection image in reflecting portions E to H of the reflector in  FIG. 9(   a ). 
     In the following description, it is assumed that a direction of an optical axis of the reflector, a transverse direction of a vehicle and a vertical direction of the vehicle over a front surface of the vehicle are set to be an X direction, a Y direction and a Z direction, respectively. The optical axis of the reflector can be grasped as a direction in which a light reflected by the reflector is set into the brightest direction, for example. Alternatively, the optical axis can also be grasped as a direction from a center of an upper edge of the reflector (an upper edge  62   a  shown in  FIG. 9(   a )) toward the front surface of the vehicle. 
     A headlamp  70  for a vehicle shown in  FIG. 9(   a ) includes a reflector  62  and a light source  64  having a linear light emitting surface with at least one side which is linear. The light source  64  is rotated around a Z axis and a linear side  64   b  is disposed obliquely to the optical axis (the X direction) as shown in  FIG. 9(   b ). Moreover, the light source  64  is disposed in such a manner that a light emitting surface  64   a  is turned downward. In other words, a light emitted downward from the light source  64  is reflected forward from the vehicle through each reflecting portion on a surface of the reflector  62  and is superposed as a projection image. The reflector  62  according to the embodiment is constituted in such a manner that rotating angles of images (projection images) E to H reflected by the light emitting surface formed by the reflecting portions E to H are different from each other as shown in  FIG. 9(   d ). 
     In other words, an angle of a long side of a projection image obtained by projecting the rectangular light source  64  in an advancing direction of the vehicle is varied on each point over the reflector  62 . In a reflecting portion in which the Y direction of the reflector  62  is varied, a light source image is reflected and projected at a different angle. Therefore, it is possible to specify a position in which a projection angle is brought into a horizontal state and a position in which the projection angle is varied from the horizontal state to a predetermined angle. 
     Accordingly, a first reflecting portion  66  for carrying out a reflection in such a manner that a linear side of an image reflected by a light emitting surface is set into the same horizontal direction as a first cut-off line is present in at least a region between reflecting portions F and G shown in  FIG. 9(   a ). A line L 1  shown in  FIG. 9(   c ) is obtained by connecting a plurality of first reflecting portions  66 . Moreover, a second reflecting portion  68  for carrying out a reflection in such a manner that a linear side of an image reflected by a light emitting surface forms a predetermined angle (approximately 15 degrees) with respect to the same horizontal direction as a second cut-off line is present in at least a region between reflecting portions G and H shown in  FIG. 9(   a ). A line L 2  shown in  FIG. 9(   c ) is obtained by connecting a plurality of second reflecting portions  68 . 
     The reflector  62  reflects a light emitted from a light source to form a light distribution pattern having the first cut-off line and the second cut-off line which have angles with respect to each other, and furthermore, takes such a shape that an area of a region on a left side in a transverse direction of the vehicle (the Y direction) and an area of a region on a right side around the optical axis (the X direction) are different from each other as shown in  FIGS. 9(   a ) and  9 ( c ). Moreover, the first reflecting portions  66  and the second reflecting portions  68  are positioned in the region on the right side which has a larger effective reflecting area as seen rearward toward the reflector  62 . 
     In the headlamp  70  for a vehicle, thus, the first reflecting portions  66  for forming the first cut-off line and the second reflecting portions  68  for forming the second cut-off line are constituted to be positioned in a region on a left side and a region on a right side which has a large area in the reflector  62 . Therefore, the headlamp  70  for a vehicle can suppress a reduction in a luminous intensity in the vicinity of the cut-off line. Thus, it is possible to form a light distribution pattern for a low beam which has an excellent distance visibility and a desirable luminous intensity. 
     Also in the case in which a reflecting surface of the reflector is symmetrical with respect to the light source depending on a design of the vehicle headlamp or a space of the vehicle for mounting, moreover, it is possible to ensure the distance visibility by disposing the light source in such a manner that the linear side of the light emitting surface is oblique to the optical axis. In other words, it is possible to form a desirable light distribution pattern for a low beam while satisfying a degree of freedom of a design of a lighting device. 
     Although the description has been given to the case in which the region on the left side in the reflector  62  is taken away as seen from a forward part (the area of the region on the right side is large) in the above embodiment, one or more embodiments of the invention can also be applied to the case in which the region on the right side is taken away (the area of the region on the left side is large). In that case, it is possible to make a correspondence by causing a rotating direction of the light source  64  to be reverse to a rotating direction R shown in  FIG. 9(   b ). 
     (Second Embodiment) 
     The headlamp  70  for a vehicle according to the first embodiment is disposed in such a manner that the light emitting surface of the light source is turned downward. The vehicle headlamp according to the embodiment is different from the headlamp  70  for a vehicle in that a light emitting surface of a light source is turned in a transverse direction of the vehicle. 
       FIG. 10(   a ) is a front view schematically showing a reflector according to a second embodiment,  FIG. 10(   b ) is a top view schematically showing the reflector according to the second embodiment,  FIG. 10(   c ) is a perspective view schematically showing the reflector according to the second embodiment, and  FIG. 10(   d ) is a side view showing a tilt of a light source according to the second embodiment. 
     A headlamp  80  for a vehicle shown in  FIG. 10(   a ) includes a reflector  72  and a light source  74  having a linear light emitting surface with at least one side which is linear. The light source  74  is rotated around a Y axis and a linear side  74   b  is disposed obliquely to an optical axis (an X direction) as shown in  FIG. 10(   d ). Moreover, the light source  74  is disposed in such a manner that a light emitting surface  74   a  is turned toward an outside in a transverse direction of a vehicle (a Y direction). In other words, a light emitted from the light source  74  in the Y direction is reflected forward from the vehicle through each reflecting portion on a surface of the reflector  72  and is superposed as a projection image. The reflector  72  according to the embodiment is constituted in such a manner that a rotating angle of an image (a projection image) reflected by a light emitting surface formed by a reflecting portion having a different Z direction is varied. 
     In other words, an angle of a long side of a projection image obtained by projecting the rectangular light source  74  in an advancing direction of the vehicle is varied on each point over the reflector  72 . In a reflecting portion in which the Z direction of the reflector  72  is varied, a light source image is reflected and projected at a different angle. Therefore, it is possible to specify a position in which a projection angle is brought into a horizontal state and a position in which the projection angle is varied from the horizontal state to a predetermined angle. 
     Accordingly, a first reflecting portion  76  for carrying out a reflection in such a manner that a linear side of an image reflected by a light emitting surface is set into the same horizontal direction as a first cut-off line is positioned on a line L 1  shown in  FIGS. 10(   a ) to  10 ( c ). Moreover, a second reflecting portion  78  for carrying out a reflection in such a manner that a linear side of an image reflected by a light emitting surface forms a predetermined angle (approximately 15 degrees) with respect to the same horizontal direction as the second cut-off line is positioned on a line L 2  shown in  FIGS. 10(   a ) to  10 ( c ). 
     The reflector  72  reflects a light emitted from a light source to form a light distribution pattern having the first cut-off line and the second cut-off line which have angles with respect to each other, and furthermore, takes such a shape that an area of a region on an upper side and an area of a region on a lower side around the optical axis (the X direction) are different from each other as shown in  FIG. 10(   a ). Moreover, the first reflecting portions  76  and the second reflecting portions  78  are positioned in the region on the lower side in which an effective reflecting area is large as seen toward a rear part of the reflector  72 . 
     In the headlamp  80  for a vehicle, consequently, the first reflecting portions  76  for forming the first cut-off line and the second reflecting portions  78  for forming the second cut-off line are positioned in a region on a lower side of the reflector  72  which has a larger area. Therefore, the headlamp  80  for a vehicle can suppress a reduction in a luminous intensity in the vicinity of the cut-off line. Thus, it is possible to form a light distribution pattern for a low beam which has an excellent distance visibility and a desirable luminous intensity. 
     Also in the case in which a reflecting surface of the reflector is vertically symmetrical with respect to the light source depending on a design of the vehicle headlamp or a space of the vehicle for mounting, moreover, it is possible to ensure the distance visibility by disposing the light source in such a manner that the linear side of the light emitting surface is oblique to the optical axis. In other words, it is possible to form a desirable light distribution pattern for a low beam while satisfying a degree of freedom of a design of a lighting device. 
     Although the description has been given to the case in which the region on the upper side in the reflector  72  is taken away as seen toward the rear part (the area of the region on the lower side is large) in the above embodiment, one or more embodiments of the invention can also be applied to the case in which the region on the lower side is taken away (the area of the region on the upper side is large). In that case, it is possible to make a correspondence by causing a rotating direction of the light source  74  to be reverse to a rotating direction R shown in  FIG. 10(   d ). 
     In accordance with the above embodiments, a vehicle headlamp may include: a light source  64  having a light emitting surface  64   a , the light emitting surface  64   a  including at least a linear side  64   b ; and a reflector  62  adapted to reflect a light emitted from the light source  64  and form a light distribution pattern PL having a first cut-off line CL 1  and a second cut-off line CL 2 , the first cut-off line CL 1  and the second cut-off line CL 2  intersect to each other with an angle. In the reflector  62 , an area of a region on a left side in a transverse direction Y of a vehicle and an area of a region on a right side in the transverse direction Y with respect to an optical axis X may be different from each other. The reflector  62  may include a plurality of first reflecting portions  66  configured to form the first cut-off line CL by images of said linear side  64   b  of the light emitting surface  64   a  reflected on the first reflecting portions  66  and a plurality of second reflecting portions  68  configured to form the second cut-off line CL 2  by images of said linear side  64   b  of the light emitting surface  64   a  reflected on the second reflecting portions  68 . The light source  64  is disposed so that said linear side  64   b  of the light emitting surface  64   a  is oblique with respect to the optical axis X and both of the first reflecting portions  66  and the second reflecting portions  68  are positioned in one of the region on the left side and the region on the right side which has a larger area. 
     According to this structure, the reflecting portions for forming the first cut-off line and the second cut-off line are positioned in either of the region on the left side and the region on the right side in the reflector which has a larger area. Therefore, it is possible to form a light distribution pattern having a desirable luminous intensity. The light source may be disposed in such a manner that the light emitting surface is turned downward. 
     Moreover, in accordance with the above embodiments, a vehicle headlamp may include: a light source  74  having a light emitting surface  74   a , the light emitting surface  74   a  including at least a linear side  74   b ; and a reflector  72  adapted to reflect a light emitted from the light source  74  and form a light distribution pattern PL having a first cut-off line CL 1  and a second cut-off line CL 2 , the first cut-off line CL 1  and the second cut-off line CL 2  intersect to each other with an angle. In the reflector  72 , an area of a region on a upper side and an area of a region on a lower side with respect to an optical axis X may be different from each other. The reflector  72  may include a plurality of first reflecting portions  76  configured to form the first cut-off line CL 1  by images of said linear side  74   b  of the light emitting surface  74   a  reflected on the first reflecting portions  76  and a plurality of second reflecting portions  78  configured to form the second cut-off line CL 2  by images of said linear side  74   b  of the light emitting surface  74   a  reflected on the second reflecting portions  78 . The light source  74  may disposed so that said linear side  74   b  of the light emitting surface  74   a  is oblique with respect to the optical axis X and both of the first reflecting portions  76  and the second reflecting portions  78  are positioned in one of the region on the upper side and the region on the lower side which has a larger area. 
     According to this structure, the reflecting portions for forming the first cut-off line and the second cut-off line are positioned in either of the region on the upper side and the region on the lower side in the reflector which has a larger area. Therefore, it is possible to form a light distribution pattern having a desirable luminous intensity. The light source may be disposed in such a manner that the light emitting surface is turned in a transverse direction of a vehicle. 
     According to the vehicle headlamp of the embodiments, it is possible to form a desirable light distribution pattern. 
     Although the invention has been described above with reference to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. The invention is not restricted to the above embodiments, and may include a combination of the structures according to the embodiments or their replacement. Moreover, modifications, for example, a combination in the embodiments, a proper rearrangement of order of processings or various changes in a design can also be made for the embodiments based on the knowledge of the skilled in the art, and an embodiment thus modified can also be included in the invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
           10  vehicle headlamp 
           22  light emitting module 
           24  reflector 
           24   a  reflecting surface 
           26  shade 
           50  light emitting device 
           52   a  light emitting surface 
           52   b  upper edge 
           60 ,  62  reflector 
           62   a  upper edge 
           64  light source 
           64   a  light emitting surface 
           66  first reflecting portion 
           68  second reflecting portion 
           70  vehicle headlamp 
           72  reflector 
           74  light source 
           74   a  light emitting surface 
           76  first reflecting portion 
           78  second reflecting portion 
           80  vehicle headlamp