Patent Publication Number: US-10323814-B2

Title: Vehicular lamp having a two-dimensional image forming device and a dimming part

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims the benefit of priority of Japanese Patent Application No. 2012-197277 filed on Sep. 7, 2012. The disclosures of the application are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a vehicular lamp to be mounted on a vehicle. 
     Related Art 
     A lighting device using a DMD (Digital Mirror Device) which includes several hundreds to hundred thousands of tiny reflective elements is disclosed in Patent Document 1. Patent Document 1 has suggested that the characteristics of the light beam emitted from the lighting device are extensively changed by each reflective element of the DMD in a simple manner. 
     Patent Document 1: Japanese Patent Laid-Open Publication No. Hei 9-104288 
     However, light from a light source is irradiated toward a projection plane on DMD while being spread to some extent. Out of light from the light source, light incident on the projection plane side in a boundary of the projection plane is reflected and projected to the front of the lamp by a projection lens. Meanwhile, light directed to the outside of the projection plane is not reflected and is not incident on the projection lens. Accordingly, in the light distribution pattern projected to the front of the lamp by the projection lens, a clear boundary line between a dark portion and a bright portion due to a boundary of the projection plane is formed and therefore a user feels a sense of discomfort. 
     SUMMARY 
     Exemplary embodiments of the invention provide a vehicular lamp which is capable of obscuring a boundary line between a bright portion and a dark portion due to a boundary of the projection plane and capable of forming a natural light distribution pattern without giving a sense of discomfort. 
     A vehicular lamp according to an exemplary embodiment of the invention, comprises:
         a projection lens;   a two-dimensional image forming device located on or in the vicinity of a rear focal point of the projection lens, and including a plurality optical elements which are arranged in a matrix shape and individually driven and a projection plane that is formed by the plurality optical elements;   a light source configured to irradiate the projection plane of the two-dimensional image forming device with light; and   a dimming part provided between the optical elements and the projection lens and configured to reduce light directed to the projection lens from the optical elements arranged on an end portion of the projection plane.       

     The vehicular lamp may comprise a transparent cover provided between the optical elements and the projection lens, wherein the dimming part is provided in an end portion of the transparent cover. 
     The dimming part may gradually reduce the light directed to the projection lens over the optical elements arranged from the central side to the end portion side of the projection plane. 
     The dimming part may reduce light directed to the projection lens by blocking a portion of light directed to the projection lens from the optical elements. 
     The dimming part may reduce light directed to the projection lens by diffusing a portion of light directed to the projection lens from the optical elements. 
     According to the present invention, since the dimming part is provided so as to correspond to the end portion of the projection plane in a two-dimensional image forming device, it is possible to reduce an amount of light to be incident on the projection lens from the reflective elements arranged on the end portion and it is possible to reduce a unnatural brightness difference of the light distribution pattern occurring due to a boundary of the projection plane. In this way, it is possible to provide a vehicular lamp which is capable of forming a light distribution pattern having a natural visual performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional side view of a vehicular headlamp according to an exemplary embodiment of the present invention. 
         FIG. 2  is a partially enlarged view of  FIG. 1 . 
         FIG. 3  is a partially enlarged view of DMD. 
         FIG. 4A  is a view showing a light distribution pattern that is formed by the vehicular headlamp according to the present embodiment,  FIG. 4B  is a view showing an irradiation pattern and a projection plane for forming the light distribution pattern of  FIG. 4A  and  FIG. 4C  is a view showing a light distribution pattern according to a comparative example. 
         FIGS. 5A and 5B  are views schematically showing a dimming part. 
         FIG. 6A  is a view showing another example of the irradiation pattern and  FIG. 6B  is a view showing a light distribution pattern that is formed using the irradiation pattern of  FIG. 6A . 
         FIG. 7  is a view showing a vehicular headlamp according to another exemplary embodiment, corresponding to  FIG. 2 . 
         FIG. 8  is a partially enlarged view of a liquid crystal device. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an example of a vehicular lamp according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  shows a sectional side view of a vehicular headlamp  1  that is an example of a vehicular lamp. The vehicular headlamp  1  includes a lamp body  2  having an opening that opens to the front of the lamp and an outer cover  3  made of transparent resin and attached to the opening. The outer cover  3  is disposed to close the opening of the lamp body  2  from the front and forms a lamp chamber S together with the lamp body  2 . In the following description, a direction of an arrow X shown in  FIG. 1  is defined as a front side that is a light irradiation direction and a direction of an arrow Y shown in  FIG. 1  is defined as an upper side. 
     In the interior of the lamp chamber S, a DMD (Digital Mirror Device)  10  as a two-dimensional image forming device, a LED  4  as a light source, a reflector  5  for reflecting light from the LED  4  toward the DMD  10  and a projection lens  6  through which light from the DMD  10  is transmitted to the front are provided. Further, in the outside of the chamber S, a control unit  7  for controlling an operation of the DMD  10  is provided. 
       FIG. 2  is an enlarged view showing each member disposed in the interior of the lamp chamber S. 
     A projection plane  11  for reflecting light from the LED  4  is formed on a front side surface of the DMD  10 . The reflector  5  includes a reflective surface  5   a  for reflecting the light emitted from the LED  4  toward the projection plane  11  of the DMD  10 . Substantially entire surface of the projection plane  11  of the DMD  10  is irradiated with the light that is emitted from the LED  4  and reflected by the reflector  5 . 
     The projection lens  6  is provided in such a way that an optical axis Ax ( FIG. 3 ) thereof is directed to a front-rear direction of the lamp. The projection lens  6  is disposed on the front side of the DMD  10  so that a position of a rear focal point F of the projection lens  6  substantially coincides with the projection plane  11  of the DMD  10 . Thereby, an irradiation pattern formed on the projection plane  11  of the DMD  10  is projected forward in a state of being vertically and horizontally inverted and enlarged. 
     A transparent cover  13  is provided between the projection plane  11  of the DMD  10  and the projection lens  6  and, in the present embodiment, on the projection plane  11  of the DMD  10 . The transparent cover  13  is a member for protecting reflective elements  12  to be described later. The transparent cover  13  is disposed to cover the projection plane  11 . Accordingly, the light reflected by the projection plane  11  is emitted to the front of the lamp through the transparent cover  13 . 
       FIG. 3  shows an enlarged view of the DMD  10 . 
     The DMD  10  is a device that is formed using an MEMS (Micro Electro Mechanical Systems) technology. The DMD  10  is a two-dimensional image forming device in which a plurality of reflective elements (which is an example of optical element)  12  are arranged on a single substrate in a matrix shape. By these reflective elements  12 , the projection plane  11  for reflecting the light emitted from the LED  4  is formed on a front surface of the DMD  10 . The DMD  10  is disposed on or in the vicinity of the rear focal point F of the projection lens  6 . 
     Each of a plurality of reflective elements  12  is provided rotatably about its rotating axis. By applying voltage individually to each reflective element  12 , each reflective element  12  can be individually switched between a state where the reflective element is stationary in a posture indicated by an arrow A and a state where the reflective element is stationary in a posture indicated by an arrow B. 
     When the reflective element  12  is in a posture indicated by the arrow A (i.e., in a posture where a reflective surface of the reflective element  12  forms an angle of about 45′ with respect to the optical axis Ax), the light L 1  incident on the reflective element  12  is reflected to be incident on the projection lens  6 . Thereby, light from the LED  4  is emitted to the front of the lamp through the projection lens  6 . The reflective element  12  is referred to be in an incident position when the reflective element  12  is in a posture where light from the LED  4  is allowed to be incident on the projection lens  6  as described above. 
     On the contrary, when the reflective element  12  is in a posture indicated by the arrow B (i.e., in a posture where a reflective surface of the reflective element  12  is substantially perpendicular to the optical axis Ax), the light L 2  incident on the reflective element  12  is not incident on the projection lens  6  but reflected in a direction deviated from the projection lens  6 . Thereby, light from the LED  4  is not emitted to the front of the lamp. The reflective element  12  is referred to be in a non-incident position when the reflective element  12  is in a posture where the light is not allowed to be incident on the projection lens  6  as described above. 
     The reflective elements  12  are driven individually by a control signal transmitted from a control unit  7  (see  FIG. 1 ) and can be respectively switched between the incident position and the non-incident position. By switching each of the reflective elements  12  between the incident position and the non-incident position, it is possible to form a desired irradiation pattern on the projection plane  11 . 
     In the vehicular headlamp  1  thus configured, an irradiation pattern  40  formed on the projection plane  11  is projected to the front of the lamp by the projection lens  6 , thereby forming a light distribution pattern  30 . Accordingly, in order to form the light distribution pattern (light distribution pattern for a low-beam)  30  as shown in  FIG. 4A  in front of the lamp, the irradiation pattern  40  as shown in  FIG. 4B  is formed on the projection plane  11 .  FIGS. 4A and 4C  show light distribution patterns  30 ,  30 A formed on a virtual vertical screen which is provided in the front of 25 m of the vehicular headlamp  1 . 
       FIG. 4B  shows an example of the irradiation pattern  40  to be formed on the projection plane  11 . As indicated by reference numeral C, the range of the projection plane  11  larger than the irradiation pattern  40  in a shape approximating to the light distribution pattern  30  is irradiated with light from the LED  4 . Furthermore, the reflective elements  12  belonging to a region of the irradiated range C corresponding to the shape of the light distribution pattern  30  are set on an incident position and the other reflective elements  12  are set on a non-incident position. In this way, by setting the reflective elements  12  belonging to a specific region on the incident position and setting the other reflective elements  12  on the non-incident position, the irradiation pattern  40  is formed on the projection plane  11 . Here, the irradiation pattern  40  refers to a shape that is configured by a plurality of reflective elements  12  to be set on the incident position. Although the reflective elements  12  are not shown in  FIG. 4B , it is preferable that ten thousands to one million of reflective elements  12  are formed on the projection plane  11 . 
     Here, light from the LED  4  is irradiated toward the projection plane  11  while being spread to some extent. Accordingly, as shown in  FIG. 4B , a portion of light from the LED  4  unintentionally is irradiated toward the outside of the projection plane  11 . 
     Then, in a case where the dimming part  15  is not provided, in the ends of the left and right direction of the irradiation pattern  40 , light from the LED  4  is reflected on the inside of the end boundary of the projection plane  11  and light from the LED  4  is not reflected on the outside of the end boundary of the projection plane  11 . That is, as in the light distribution pattern  30 A of a comparative example shown in  FIG. 4C , a bright portion  30 A 1  that is brightly irradiated with reflection light from the reflective elements  12  is formed on the inside of the light distribution pattern  30 A and a dark portion  30 A 2  that is not irradiated with light is formed on the outside of the light distribution pattern  30 A, in the ends of the left and right direction of the light distribution pattern  30 A. Accordingly, an extreme light-dark boundary line D is visually recognized at the contour of the light distribution pattern  30 A and thus a user feels a sense of discomfort. Such a sense of discomfort is more noticeable when a light-dark boundary line of the light distribution pattern  30 A appears as a linear shape, as illustrated. 
     Accordingly, in the present embodiment, the dimming part  15  is provided between the reflective elements  12  and the projection lens  6  and reduces light directed to the projection lens  6  from the reflective elements  12  arranged in the end portion of the projection plane  11 . In the example shown in  FIG. 4B , the dimming part  15  of a frame shape including an outermost periphery of the projection plane  11  is provided on the transparent cover  13 . Since the dimming part  15  is provided in a site covering the reflective elements  12  disposed in the outermost periphery, it is possible to reduce light directed to the projection lens  6  from at least the reflective elements  12  disposed in the outermost periphery of the projection plane  11 . 
     Such a dimming part  15  can be formed by printing ink of semi-translucency on a site of an upper surface of the transparent cover  13  that covers the reflective elements  12  to be dimmed, for example. Alternatively, the dimming part  15  can be configured by collection of fine dots that are obtained by printing ink of light shielding property on the transparent cover  13 , or a semi-transparent tape affixed to the transparent cover  13 , or the like. 
     Alternatively, the dimming part  15  may be configured by diffusing light so as not to be directed to the projection lens  6  as well as blocking a portion of light to be incident on the projection lens  6 . In this case, the dimming part  15  may be configured by providing a diffusion prism at a site of an upper surface of the transparent cover  13  that covers the reflective elements  12  to be dimmed or forming fine irregularities on the upper surface of the transparent cover  13 . 
     As such, according to the vehicular headlamp  10  of the present embodiment, light directed to the projection lens  6  from at least the reflective elements  12  positioned at an outermost periphery of the projection plane  11  is reduced by the dimming part  15 . As a result, intensity of light in end portions  32  of the light distribution pattern  30  is weaker than that in a center portion  31  of the light distribution pattern  30  and therefore it is possible to blur a light-dark boundary line in the end portion of the light distribution pattern  30 , thereby forming the light distribution pattern  30  having a natural visual performance. 
     As illustrated, the dimming part  15  may be formed in a frame shape having a predetermined width so that light from the reflective elements  12  located inside the reflective elements  12  positioned at the outermost periphery of the projection plane  11  can be also reduced together. In this case, it is preferable to form the dimming part  15  in such a way that an amount of dimming of light from the reflective elements  12  positioned at the central side of the projection plane  11  is smaller than that of light from the reflective elements  12  positioned at an outer periphery side of the projection plane  11 . 
     Further, it is desirable to gradually reduce the light directed to the projection lens  6  over the reflective elements  12  arranged from the central side to the end portion side of the projection plane  11 . In the present embodiment, the dimming part  15  includes a first dimming portion  15   a  covering at least the reflective elements  12  positioned at the outermost periphery of the projection plane  11  and a second dimming portion  15   b  provided inside the first dimming portion  15   a . The second dimming portion  15   b  is formed in such a way that an amount of dimming of the second dimming portion becomes smaller than that of the first dimming part  15   a . As a result, intensity of light is weakened step by step from an inner side toward an outer side of the light distribution pattern  30  and therefore it is possible to form the light distribution pattern  30  having a visual performance which is more natural to a user. 
     Further, the shape of the dimming part  15  is not limited to the frame shape shown in  FIG. 4B . The dimming part  15  may be formed in order to block light directed to the projection lens  6  from at least some reflective elements  12  positioned at the outermost periphery of the projection plane  11 . For example, as shown in  FIG. 5A or 5B , the dimming part  15  may be formed in order to reduce light directed to the projection lens  6  from the reflective elements  12  positioned at both left and right end portions of the projection plane  11  as seen from the front of the lamp. 
     In  FIG. 5A , the dimming part  15  is configured by a plurality of spots which are obtained by printing ink of semi-translucency in the vicinity of the left and right end portions of the projection plane  11 . Each of these spots is formed in such a way that each spot is larger in the end portion side and becomes smaller toward the center. As a result, light from the reflective elements  12  disposed in an outer periphery side of the projection plane  11  is greatly blocked by the dimming part  15  and a blocked degree of light from the reflective elements  12  disposed in the center side is gradually reduced. Thereby, it is possible to form the light distribution pattern  30  having a natural visual performance, in which brightness is gradually lowered from the center toward the outside and thus the light-dark boundary line D is not conspicuous. 
     Further, as shown in  FIG. 5B , ink of semi-translucency may be printed in a triangular shape protruding toward the central side from the end portion of the projection plane  11 . According to this example, it is possible to achieve the same effects as in the dimming part  15  shown in  FIG. 5A . 
     The dimming part  15  may not be provided on the transparent cover  13 . On the path of light directed to the projection lens  6  from the reflective elements  12 , the dimming part  15  may be configured by a member different from the transparent cover  13 . For example, the dimming part  15  may be configured by providing a semi-transparent plate or a diffusion prism or the like on the path of light directed to the projection lens  6  from the reflective elements  12 . 
       FIG. 6A  shows irradiation patterns  41 ,  42  of another example to be formed on the projection plane  11 . Further,  FIG. 6B  shows a light distribution pattern (light distribution pattern for a high beam)  50  which is formed by the irradiation patterns  41 ,  42  shown in  FIG. 6A . 
     In the example shown in  FIG. 6A , the range C of light to be incident on the projection plane  11  from the LED  4  is adapted to cover substantially entire surface of the projection plane  11  in order to be able to make effective use of the projection plane  11 . Further, the projection plane  11  is divided into two projection regions  11   a ,  11   b  of the upper and lower. Here, an irradiation pattern  41  forming the right side  50 R of the light distribution pattern  50  is formed in an upper projection region  11   a  and an irradiation pattern  42  forming the left side  50 L of the light distribution pattern  50  is formed in a lower projection region  11   b . The projection lens  6  projects the irradiation patterns  41 ,  42  forward so as to be continuous in the left and right direction. As a result, the light distribution pattern  50  that is long in the left and right direction as shown in  FIG. 6B  is formed. At this time, the end portions  41   a ,  41   b  of the irradiation patterns  41 ,  42  are projected in a state of being overlapped with each other. 
     Here, in a case where the dimming part is not provided, a light-dark boundary line is conspicuous when the light distribution pattern is formed by overlapping the end portions of the irradiation patterns. That is, when intensity of light to be irradiated by each irradiation pattern  41 ,  42  is defined as 100, illuminance is 200 in a central region  52  of the light distribution pattern in which the irradiation patterns  41 ,  42  are overlapped. Further, in an outer region  51  of the left and right of the light distribution pattern, the irradiation patterns are not overlapped and therefore illuminance is 100. As a result, a light-dark boundary line D formed at a boundary between the region  52  of illuminance  200  and the region  51  of illuminance  100  is conspicuous. 
     However, according to the vehicular headlamp  1  of the present embodiment, illuminance in the end portions  41   a ,  42   a  of the irradiation patterns  41 ,  42  is reduced by the dimming part  15 , even when the light distribution pattern  50  is formed by overlapping the irradiation patterns  41 ,  42 . For this reason, brightness of the overlapped portion  52  is not twice brightness of the region  51  that is not overlapped. In this way, it is possible to allow the light-dark boundary line D to be inconspicuous. 
     More preferably, an amount of dimming of the dimming part  15  is set so that brightness is varied linearly from a bright region toward a dark region. As a result, in a central region  52  of the light distribution pattern  50 , light with illuminance  50  is overlapped and therefore illuminance  100  is obtained. Also in an outer region  51  of the left and right of the light distribution pattern  50 , illuminance  100  is obtained. Thereby, it is possible to form a light distribution pattern in which a light-dark boundary line D is not formed and which has an extremely natural visual performance. 
     Although the DMD  10  is used as a two-dimensional image forming device in the above-described embodiment, the present invention is not limited to this configuration. For example, a liquid crystal device may be used as a two-dimensional image forming device.  FIG. 7  shows the members in an interior of the lamp chamber S when a liquid crystal device  60  is used as a two-dimensional image forming device. 
     In the interior of the lamp chamber S, the LED  4 , the liquid crystal device  60  and the projection lens  6  are arranged in order from the rear in a direction of the optical axis Ax. A projection plane  61  through which light from the LED  4  can be transmitted is formed on a front side surface (a projection lens  6  side) of the liquid crystal device  60 . An irradiation pattern formed on the projection plane  61  of the liquid crystal device  60  is projected forward by the projection lens  6 , in a state of being vertically and horizontally inverted and enlarged. 
       FIG. 8  shows an enlarged view of the liquid crystal device  60 . 
     A plurality of liquid crystal elements (optical elements)  62  are arranged on the projection plane  61  of the liquid crystal device  60  in a matrix shape. The projection plane  61  through which light from the LED  4  is transmitted is formed by these liquid crystal elements  62 . Further, a glass cover (transparent cover)  63  for protecting the liquid crystal elements  62  is attached to the projection plane  61 . The liquid crystal elements  62  are separately enclosed between the glass cover  63  and a transparent electrode  64  in a matrix shape. 
     The liquid crystal elements  62  can be individually switched between a transmissive state (a state indicated by an arrow A) where light from the LED  4  is transmitted through the liquid crystal elements and allowed to be incident on the projection lens  6  and a non-transmissive state (a state indicated by an arrow B) where light from the LED  4  is blocked by the liquid crystal elements and not allowed to be incident on the projection lens  6 . By switching each of the liquid crystal elements  62  between the transmissive state and the non-transmissive state, it is possible to form a desired irradiation pattern on the projection plane  61 . 
     A dimming part  65  is provided at a site of the glass cover  63  that covers at least the liquid crystal elements  62  arranged on an end portion of the projection plane  61  and diminishes the light directed to the projection lens  6  from the liquid crystal elements  62  arranged on the end portion of the projection plane  61 . 
     Even in a case where the liquid crystal device  60  is used as a two-dimensional image forming device as described above, it is possible to reduce the amount of light incident toward the projection lens  6  from the liquid crystal elements  62  arranged in a peripheral portion of the projection plane  61  by providing the dimming part  65  in a peripheral portion of the glass cover  63 . As a result, it is possible to form a light distribution pattern having a natural visual performance, in which intensity of light is gradually attenuated toward an outer periphery thereof and thus a light-dark boundary line is not conspicuous, in an end portion of a light distribution pattern to be projected from the projection lens  6 . 
     Although an example where the present invention is applied to a vehicular headlamp has been described in the above description, the present invention is not limited to this configuration. For example, the present invention may be applied to a vehicular signaling lamp or the like. Further, although an example where LED is employed as a light source has been described, an organic EL or discharge bulb or the like may be employed as the light source. In addition, although a light distribution pattern for a low beam and a light distribution pattern for a high beam have been described as an example of the light distribution pattern to be formed, the present invention is not limited to these light distribution patterns.