# Patent

## Title
Vehicle lighting unit

## Abstract

A vehicle lighting unit can be configured to include a thin light guide. The vehicle lighting unit can include a solid light guide having a first surface including an internal reflection portion and a light exiting portion that are formed as a single continued surface, a second surface opposite to the first surface, and a light incident surface through which light enters the light guide so that the light reaches and is internally reflected off the internal reflection portion of the first surface, then is internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface. The reflection portion of the second surface can include a plurality of divided reflection regions, and the reflection regions can include at least one reflection region disposed at a reference position and at least one reflection region disposed at a position closer to the light exiting surface than the reference position.

## Background
This application is a continuation in part and claims the priority benefit under 35 U.S.C. §120 of U.S. patent application Ser. No. 13/430,669 filed on Mar. 26, 2012 and which claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2011-068270 filed on Mar. 25, 2011, each disclosure of which is hereby incorporated in its entirety by reference.


TECHNICAL FIELD
The presently disclosed subject matter relates to a vehicle lighting unit, and in particular to a vehicle lighting unit including a light guide and an LED light source in combination.
BACKGROUND ART
Conventionally, there have been various lighting units proposed including a light guide and an LED light source in the technical field of vehicular lighting units (for example, see Japanese Patent No. 4339028 or corresponding U.S. Pat. No. 7,070,312).
FIG. 1 shows a lighting unit 90 described in Japanese Patent No. 4339028, which can include a transparent resin light guide 91 and an LED light source 92.
The light guide 91 can be configured such that light emitted from the LED light source 92 can enter the inside of the light guide 91, be reflected off the front surface 91a and reflected off the rear surface 91b, thereby being projected forward from the front surface 91a. 
The lighting unit 90 has the front surface 91a of the light guide 91 being a plane surface and the rear surface 91b opposite thereto being a continuous surface (for example, revolved paraboloid), and accordingly, the thickness between the front and rear surfaces 91a and 91b becomes large. This may increase the molding time for the light guide 91 and the amount of a transparent resin material, thereby resulting in cost increase. In general, the molding time for a molded article may be proportional to the square of the thickness of the molded article.
In addition, when the thickness is large, shrinkage or the like giving adverse effects on the accuracy of the light guide 91 (by extension, light distribution) may be likely to occur. There may be another problem due the large thickness (namely, the optical path length in the light guide 91 may be longer) wherein the light entering the light guide may be likely to be affected by the absorption of the transparent resin material or haze (volume scattering). In order to reduce such adverse effects like the absorption of the transparent resin material or haze (volume scattering), it has been a consideration to shorten the optical path length in the light guide 91. However, this has been achieved by miniaturization of the entire size of the light guide 91, resulting in decrease of the light utilization efficiency and the like.
Further, the lighting unit 90 as described above may have a problem of lower degree of freedom with regard to the formation of light distribution because the rear surface 91b of the light guide 91 is a continuous surface (revolved paraboloid, for example). In order to cope with this problem, a plurality of lighting units 90 each forming different light distribution are combined to synthesize a desired light distribution pattern as disclosed in the above patent literature.
SUMMARY
The presently disclosed subject matter was devised in view of these and other problems and features and in association with the conventional art. According to an aspect of the presently disclosed subject matter, a vehicle lighting unit can include a light guide thinner than the conventional one.
According to another aspect of the presently disclosed subject matter, a vehicle lighting unit can improve the degree of freedom to form light distribution.
According to still another aspect of the presently disclosed subject matter, a vehicle lighting unit can include: a solid light guide having a first surface, a second surface opposite to the first surface and including a reflection portion, and a light incident surface through which light enters the light guide, the first surface including an internal reflection portion and a light exiting portion that are formed as a single continued surface, the light guide configured such that light entering via the light incident surface reaches and is internally reflected off the internal reflection portion of the first surface, then internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface; and an LED light source disposed to face forward and obliquely downward with respect to the optical axis and towards the light incident surface, is internally reflected off the reflection portion of the first surface, is internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface, wherein the light is emitted from the LED light source within a predetermined range and enters the light guide through the light incident surface, is internally reflected off the internal reflection portion of the first surface, is internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface within a predetermined range, and light entering the light guide at an uppermost position among the light entering the light guide exits through the light exiting portion of the first surface above a reference point where light exiting the light guide at a lowermost position is present.
In the vehicle lighting unit with the above configuration, the reflection portion of the second surface can include a plurality of divided reflection regions. The reflection regions can include at least one reflection region disposed at a reference position and at least one reflection region disposed at a position closer to the light exiting portion of the first surface than the reference position.
With the above configuration, since the certain reflection region can be disposed (shifted) at the position closer to the light exiting portion of the first surface than the reference position, the thickness of the light guide can be thinned by that amount corresponding to the shift.
Further, since the thinning of the thickness of the light guide can be achieved with ease, the molding time for the light guide and the amount of a transparent resin material used for the light guide can be reduced, thereby suppressing cost.
In addition, since the thinning of the thickness of the light guide can be achieved with ease, the shrinkage or the like that may adversely affect the accuracy of the light guide (light distribution by extension) can be prevented from occurring.
Furthermore, since the thinning of the thickness of the light guide can be achieved with ease, i.e., the optical path length in the light guide can be shortened, the adverse effects due to the absorption of the transparent resin material or haze (volume scattering) can be suppressed.
Accordingly, with the above configuration, a vehicle lighting unit with a thinner light guide as compared to the conventional ones can be provided.
Further, since the certain reflection region(s) out of the plurality of divided reflection regions can be shifted closer to the light exiting portion of the first surface, the vehicle lighting unit with a novel appearance wherein a step can be observed between the reflection regions can be provided.
In the vehicle lighting unit with any of the above configurations, the reflection portion of the second surface can be divided into the plurality of reflection regions by at least one horizontal plane.
If the certain reflection region out of the plurality of reflection regions divided by the at least one horizontal plane is disposed at a position shifted closer to the light exiting portion of the first surface, the light guide can be thinned by that amount (corresponding to the shift amount).
In the vehicle lighting unit with any of the above configurations, the reflection portion of the second surface can be divided into the plurality of reflection regions by at least one vertical plane.
If the certain reflection region out of the plurality of reflection regions divided by the at least one vertical plane is disposed at a position shifted closer to the light exiting portion of the first surface, the light guide can be thinned by that amount (corresponding to the shift amount).
In the vehicle lighting unit with any of the above configurations, the reflection portion of the second surface can be divided into the plurality of reflection regions by at least two vertical planes, and the reflection regions between the two vertical planes can be disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.
If the certain reflection region out of the plurality of reflection regions divided by the at least two vertical planes and positioned between the at least two vertical planes is disposed at a position shifted closer to the light exiting portion of the first surface, the light guide can be thinned by that amount (corresponding to the shift amount).
In the vehicle lighting unit with any of the above configurations, the plurality of reflection regions can be disposed at a position shifted closer to the light exiting portion of the first surface as the reflection region is closer to the light incident surface.
Since the reflection region can be disposed at a position shifted closer to the light exiting portion of the first surface as the reflection region is closer to the light incident surface, the light internally reflected can be prevented from entering a step appearing between the adjacent reflection regions.
In the vehicle lighting unit with any of the above configurations, the plurality of reflection regions each can form a light distribution pattern part constituting a desired light distribution pattern formed by the light projected through the light exiting portion of the first surface.
With this configuration, when compared with a conventional case in which the reflection surface is a continuous surface (revolved paraboloid), the reflection surface is divided into the plurality of reflection regions each capable of forming a particular light distribution pattern part. This can give a higher degree of freedom for forming the light distribution for the vehicle lighting unit.
In the vehicle lighting unit with any of the above configurations, the light internally reflected off the plurality of reflection regions of the second surface and projected through the light exiting portion of the first surface can be configured to be not parallel with each other and with the optical axis in part. In this case, the directions of the light projected through the light exiting portion of the first surface can be spread within a horizontal plane or vertical plane.
This configuration can form a wider or narrower light distribution pattern as desired to give a higher degree of freedom for forming the desired light distribution patterns for the vehicle lighting unit.
In the vehicle lighting unit with any of the above configurations, the reflection portion of the second surface can include at least a first reflection portion and a second reflection portion that are vertically adjacent to each other. The first reflection portion of the reflection portion of the second surface is capable of reflecting light that is projected through the light exiting portion of the first surface at a position above the reference point where the light exiting the light guide at the lowermost position is internally reflected off the internal reflection portion of the first surface, and the second reflection portion of the reflection portion of the second surface is capable of reflecting light that is projected through the light exiting portion of the first surface at a position below the reference point where the light exiting the light guide at the lowermost position is internally reflected off the internal reflection portion of the first surface, so that the light reflected off the first reflection portion and the light reflected off the second reflection portion can illuminate different areas.
According to an aspect of the presently disclosed subject matter, there can be provided a vehicle lighting unit that includes a light guide thinner than the conventional one. In addition, there can be provided a vehicle lighting unit that improves the degree of freedom for forming light distribution.



BRIEF DESCRIPTION OF DRAWINGS
These and other characteristics, features, and advantages of the presently disclosed subject matter will become clear from the following description with reference to the accompanying drawings, wherein:
FIG. 1 is a cross-sectional view of a conventional example;
FIGS. 2A and 2B are a cross-sectional side view and a plan view of a vehicle lighting unit of one exemplary embodiment made in accordance with principles of the presently disclosed subject matter, respectively;
FIGS. 3A to 3D are diagrams illustrating how to determine the rear surface shape of a light guide in the exemplary embodiment;
FIGS. 4A and 4B are a schematic cross-sectional side view and a plan view of a vehicle lighting unit in the exemplary embodiment, illustrating the light emission state, respectively;
FIG. 5 is a schematic cross-sectional side view of a vehicle lighting unit of a modification of the present exemplary embodiment;
FIGS. 6A and 6B are cross-sectional views taken along line II-II and line III-III in FIG. 5, respectively;
FIGS. 7A, 7B, and 7C are diagrams illustrating how to determine the rear surface shape of a light guide in the modification of the exemplary embodiment;
FIGS. 8A, 8B, and 8C are diagrams illustrating the states where the rear surface conditions of the light guide are not met in the modification of the exemplary embodiment;
FIGS. 9A and 9B are a plan view of a vehicle lighting unit and a diagram showing a light distribution pattern formed thereby when the front surface of the light guide is convex, respectively;
FIGS. 10A and 10B are a plan view of a vehicle lighting unit and a diagram showing a light distribution pattern formed thereby when the front surface of the light guide is concave, respectively;
FIG. 11 is a perspective view illustrating another exemplary vehicle lighting unit;
FIGS. 12A, 12B, and 12C are a cross-sectional view taken along line A-A, a cross-sectional view taken along line B-B, and a perspective view when viewed from rear side, of the vehicle lighting unit shown in FIG. 11, respectively;
FIGS. 13A and 13B are longitudinal cross-sectional views of another exemplary vehicle lighting unit and the vehicle lighting unit (the original exemplary embodiment), respectively;
FIG. 14 is a longitudinal cross-sectional view (including optical paths) of the vehicle lighting unit of FIG. 11;
FIGS. 15A and 15B are a diagram showing light distribution pattern parts A1 to A3, B1 to B3, and C1 to C3 corresponding to individual reflection regions a1 to a3, b1 to b3, and c1 to c3, and a diagram showing the synthesized light distribution pattern synthesizing these light distribution pattern parts A1 to A3, B1 to B3, and C1 to C3, respectively;
FIGS. 16A, 16B, and 16C are a perspective view when viewed from front side, a perspective view when viewed from rear side, and a longitudinal cross-sectional view of a vehicle lighting unit;
FIGS. 17A, 17B, 17C, and 17D are a perspective view when viewed from a front side, a longitudinal cross-sectional view, and a perspective view when viewed from a rear side of another exemplary vehicle lighting unit, and a comparative example;
FIG. 18 is a longitudinal cross-sectional view (including optical paths) of another exemplary vehicle lighting unit;
FIG. 19 is a longitudinal cross-sectional view (including optical paths) of another exemplary vehicle lighting unit;
FIGS. 20A, 20B, and 20C are each a diagram showing the synthesized light distribution pattern obtained by synthesizing the light distribution pattern parts A1 to A3, B1 to B3, and C1 to C3 derived from the vehicle lighting unit of FIGS. 18 and 19; and
FIG. 21 is a longitudinal cross-sectional view illustrating the relationship between the optical paths and the first and second reflection portions of the reflection portion of the second surface of the light guide of another exemplary vehicle lighting unit.



DESCRIPTION OF EXEMPLARY EMBODIMENTS
A description will now be made below to vehicle lighting units of the presently disclosed subject matter with reference to the accompanying drawings in accordance with exemplary embodiments.
A vehicle lighting unit 1 of the present exemplary embodiment can constitute a vehicle headlamp to be installed on the right and left sides of the vehicle front body.
FIGS. 2A and 2B are a cross-sectional side view and a plan view of the vehicle lighting unit 1 of the present exemplary embodiment, respectively.
As shown in these drawings, the vehicle lighting unit 1 can include a light source 2 and a light guide 3 so as to project light along an optical axis Ax (extending in the front to rear direction of a vehicle body) forward.
The light source 2 can be a white LED light source including a blue LED chip and a phosphor in combination, for example. The light source 2 can be disposed such that the light source 2 can emit light in a direction inclined with respect to the optical axis Ax. Specifically, the light source 2 (light emission surface 21) can be directed along and evenly about a center emission axis forward and obliquely downward such that the angle θ formed between the center emission axis of the light emission direction of the light source and the optical axis Ax in the vertical cross-section can be 45 degrees±10 degrees.
The light guide 3 can be a light-transmitting member disposed forward and obliquely downward with respect to the light source 2. The light guide 3 can be configured to receive light from the light source 2 to project the light having become parallel to the optical axis Ax as a result of light guiding.
The light guide 3 can have a light incident surface 31 at its upper rear portion, the light incident surface 31 capable of receiving light therethrough from the light source 2. The light incident surface 31 can be opposite to the light emission surface 21 of the light source 2 with a certain gap and parallel to the light emission surface 21, namely, be inclined by an angle of 45 degrees±10 degrees with respect to the optical axis Ax in the vertical cross-section as shown in the drawing.
The light guide 3 can further have a light exiting surface 34 on its front surface 3a (being a first surface (3a) including an internal reflection portion (32) and a light exiting portion (34)). The light exiting surface 34 can be a plane extending along the vertical and horizontal directions. The light exiting surface 34 can serve as a first reflection surface 32 (inner surface) for internally reflecting the light entering through the light incident surface 31 rearward.
The light guide 3 can further have a second reflection surface 33 on its rear surface 3b (being a second surface (3b) including a second reflection portion (33)). The second reflection surface 33 can be a curved surface toward the lower end of the front surface 3a and be configured to internally reflect the light having internally reflected by the first reflection surface 32 toward the light exiting surface 34 while converting it to parallel light along and about the optical axis Ax.
Accordingly, the light guide 3 can be a solid light guide lens including the light incident surface 31 for receiving light from the light source 2, the light exiting surface 34 serving also as the first reflection surface 32 for reflecting the light rearward, and the second reflection surface opposite to the light exiting surface 34 while being inclined with respect to the light exiting surface 34. The light entering the light guide 3 through the light incident surface 31 can be internally reflected off the first reflection surface 32 at the light exiting surface 34 rearward and can travel to the second reflection surface 33, and then can be internally reflected off the second reflection surface 34 to be parallel to each other, and finally can exit through the light exiting surface 34. The light guide 3 can be formed by injection molding a transparent resin material such as an acrylic resin, a polycarbonate, a cycloolefine polymer, and the like.
Here, a description will be given of how to determine the rear surface 3b or the second reflection surface 33 of the light guide 3 while describing the vertical cross sectional shape.
First, as shown in FIG. 3A, assume that the light emitted from the light source 2 within a predetermined range can enter the light guide 3. In this case, while taking the refraction at the light incident surface 31 into consideration, the light rays are traced up to the front surface 3a of the light guide 3.
Next, as shown in FIG. 3B, assume that the light rays are totally reflected off the front surface 3a or the first reflection surface 32 of the light guide 3, and the light rays are traced.
Then, as shown in FIG. 3C, assume that a predetermined starting point P is defined on the rear surface of the light guide 3. In this case, the inclined angle at the reflection point R can be determined so that the top traced light ray can be totally reflected at that point forward in parallel to the optical axis Ax.
Next, the inclined angle at the next reflection point, that is positioned on the straight line as determined by the inclined angle at the reflection point R and crossing the second top traced light ray, can be determined so that the second top traced light ray can be totally reflected at the point forward in parallel to the optical axis Ax.
In the same manner, as shown in FIG. 3D, all the inclined angles and the crossing points (reflection points) of light rays can be sequentially determined, and these points can be connected sequentially from the light incident surface 31 to the lower end of the front surface 3a by a continuous curve or a spline curve.
In this manner, the rear surface 3b in the vertical cross-sectional shape can be determined with respect to the front-to-rear direction. Note that the light guide 3 of the present exemplary embodiment can have the rear surface 3b extending in the horizontal direction, and accordingly, any vertical cross-section along the front-to-rear direction can satisfy the same light guiding conditions if the light rays as shown in FIG. 3B enter the light guide 3.
In the vehicle lighting unit 1 with the above configuration, as illustrated in FIG. 4A, the light can be emitted from the light source 3 forward and obliquely downward with respect to the optical axis Ax and enter the light guide 3 through the light incident surface 31. The light can be internally reflected off the front surface 3a or the first reflection surface 32 of the light guide 3 rearward, and again be internally reflected off the rear surface 3b or the second reflection surface 33 forward while becoming parallel to the optical axis Ax, and then be projected through the front surface 3a or the light exiting surface 34 of the light guide 3. Accordingly, the vehicle lighting unit 1 can provide parallel light along the optical axis Ax.As described, in the vehicle lighting unit 1 of the present exemplary embodiment, since the light source 2 can emit light forward and obliquely downward with respect to the optical axis Ax, there is no need to dispose a light guide in front of the light source while the light guide extends in the vertical direction as in the conventional vehicle lighting unit in which a light source emits light forward. In the present exemplary embodiment, the light guide 3 can be disposed forward and obliquely downward with respect to the light source 2, and accordingly, the light from the light source 2 can be efficiently taken in the light guide 3. In addition, when compared with the conventional vehicle lighting unit, the light guide can be configured with a compact vertical dimension.
As a result, the thickness variation of the light guide 3 can be smaller than in the conventional ones, thereby improving the molding accuracy of the light guide 3. By extension, the molding cost can be reduced.
The light that has entered the light guide 3 can be internally reflected off the first reflection surface 32 rearward, and again be internally reflected off the second reflection surface 33 forward while becoming parallel to the optical axis Ax, and then be projected through the light exiting surface 34 of the light guide 3. Namely, the light guide 3 can internally reflect the light twice in the front or rear direction before exiting through the light exiting surface 34. The conventional light guide can internally reflect light once. Accordingly, the light guide 3 can be configured with compact dimension in the front-to-rear direction.
Further, since the light incident surface 31 of the light guide 3 can face towards the light source 2 with a certain gap therebetween, the effect of the heat generated from the light source 2 to the light guide 3 can be reduced when compared with the conventional case wherein the light source is in contact with the light guide.
<Modification 1>
Next, a description will be given of a modification 1 of the present exemplary embodiment. Note that the same as or similar components to the above exemplary embodiment are denoted by the same reference numerals, and a redundant description therefor will be omitted here.
FIG. 5 is a schematic cross-sectional side view of a vehicle lighting unit lA of the present modification, and FIGS. 6A and 6B are cross-sectional views taken along line II-II and line III-III in FIG. 5, respectively.
As shown in the drawings, the vehicle lighting unit 1A can include a light guide 3A in place of the light guide 3 of the above exemplary embodiment.
The light guide 3A can have a curved front surface 3c curved in the vertical direction and horizontal direction, rather than the flat front surface 3a. In response to the curved front surface 3c, the light guide 3A should have a rear surface 3d differently curved from the rear surface 3b of the above exemplary embodiment.
Here, a description will be given of how to determine the rear surface 3d or the second reflection surface 33 of the light guide 3A while describing the vertical cross sectional shape.
First, as shown in FIG. 7A, assume that the light emitted from the light source 2 within a predetermined range can enter the light guide 3A. In this case, while taking the refraction at the light incident surface 31 into consideration, the light rays are traced up to the front surface 3c of the light guide 3A. Further, assume that the light rays are totally reflected off the front surface 3c or the first reflection surface 32 of the light guide 3A, and the light rays are traced.
Then, as shown in FIG. 7B, while taking the refraction at the front surface 3c (or the light exiting surface 34), the parallel light rays to be emitted through the front surface 3c are traced reversely up to the rear side of the light guide 3A.
Next, as shown in FIG. 6C, the crossing points between the light rays traced from the light source 2 and the light rays reversely traced from the front surface 3c are obtained. Then, the inclined angles at respective crossing points are determined so that the light rays are totally reflected at the respective crossing points (reflection points).
All the inclined angles and the crossing points (reflection points) of light rays can be sequentially determined, and these points can be connected sequentially from the light incident surface 31 to the lower end of the front surface 3c by a continuous curve or a spline curve.
In this manner, the rear surface 3d in the vertical cross-sectional shape can be determined with respect to the front-to-rear direction.
Note that if the curvature of the front surface 3c is excessively large and, as shown in FIG. 7A, the adjacent traced light rays (assumed light rays) cross with each other, the rear surface 3d cannot be designed. Namely, in this case, even when the respective reverse-traced light rays from the front surface 3c do not cross with each other as shown in FIG. 7B, there would be a case where the respective crossing points cannot be connected with a spline curve while the inclination angles at respective crossing points satisfy the conditions of total reflection as shown in FIG. 7C. Accordingly, in order to satisfy the conditions of total reflection at the rear surface 3d, it is necessary for the respective adjacent light rays to reach the rear surface 3d with wider angles rather than parallel to each other. Thus, the front surface 3c must satisfy these conditions. Off course, when the light incident surface 31 is curved, the light incident surface 31 must satisfy the same conditions.
The vehicle lighting unit 1A with the above configuration can provide the same advantageous effects as those of the vehicle lighting units 1 of the above exemplary embodiment.
<Modification 2>
Next, a description will be given of a modification 2 of the present exemplary embodiment.
FIG. 11 is a perspective view illustrating a vehicle lighting unit 1B as a modification 2, and FIGS. 12A, 12B, and 12C are a cross-sectional view taken along line A-A, a cross-sectional view taken along line B-B, and a perspective view when viewed from rear side, of the vehicle lighting unit 1B shown in FIG. 11, respectively.
The vehicle lighting unit 1B of the modification 2 can have the same configuration as that of the above exemplary embodiment, except that the second reflection surface 33 of the light guide 3B can include a plurality of reflection regions a1 to a3, b1 to b3, and c1 to c3 divided by two horizontal planes and two vertical planes parallel to the optical axis Ax. Note that the number of the planes for dividing the surface is not limited to two, but one or three or more planes (vertical and/or horizontal planes) can be employed.
The plurality of reflection regions a1 to a3, b1 to b3, and c1 to c3 can be configured such that the reflection region can be disposed closer to the light exiting surface 34 as the reflection region is closer to the light incident surface 31. For example, as shown in FIG. 11B, the reflection regions a3, b3, and c3 can be configured such that the reflection region b3 is disposed at a position shifted closer to the light exiting surface 34 than the reflection region c3 that is disposed at the reference position as the above exemplary embodiment, and the reflection region a3 is disposed at a position shifted closer to the light exiting surface 34 than the reflection region b3. The same conditions are applied to the other rows. In this manner, the steps d1 and d2 can appear between the adjacent reflection regions.
In the modification 2, the reflection regions a2, b2, and c2 positioned between the two vertical planes can be disposed at respective positions shifted closer to the light exiting surface 34 than the adjacent reflection regions a1 to c1 and a3 to c3. For example, as shown in FIG. 11A, the reflection regions a1 to a3 can be configured such that the reflection region a2 is disposed at a position shifted closer to the light exiting surface 34 than the adjacent reflection regions a1 and a3. The same conditions are applied to the other rows. In this manner, the steps d3 and d4 can appear between the adjacent reflection regions.
FIGS. 13A and 13B are longitudinal cross-sectional views of the vehicle lighting unit 1B (modification 2) and the vehicle lighting unit 1 (the exemplary embodiment), respectively.
As shown in these drawings, the maximum inscribed circle C1 in FIG. 13A is smaller than the inscribed circle C2 in FIG. 13B, meaning that the thickness of the light guide 3B of the modification 2 is thinner than the light guide 3 of the above exemplary embodiment. (The maximum thickness portion of the modification 2 is thinner than that of the above exemplary embodiment.)
As shown, the modification 2 can be configured such that the reflection region among the plurality of divide reflection regions a1 to a3, b1 to b3, and c1 to c3 can be disposed at a position shifted closer to the light exiting surface 34 with reference to the reference position as the reflection region is closer to the light incident surface 31. Further, the reflection regions a2, b2, and c2 between the two vertical planes can be disposed at respective positions shifted closer to the light exiting surface 34. In this manner, the thickness of the light guide 3 can be thinned more. Accordingly, the molding time for the light guide 3B can be optimized.
Further, since the thinning of the thickness of the light guide 3B can be achieved in the modification 2, the molding time for the light guide 3B and the amount of a transparent resin material used for the light guide 3B can be reduced, thereby suppressing cost.
In addition, since the thinning of the thickness of the light guide 3B can be achieved with ease in the modification 2, the shrinkage or the like that may adversely affect the accuracy of the light guide 3B (light distribution by extension) can be prevented from occurring. This can improve the accuracy of the light guide 3B, and also light distribution by extension, thereby suppressing the generation of unintended unnecessary light.
Further, in the modification 2 as shown in FIG. 14, the light from the light source 2 can enter the light guide 3B and exit through the light exiting surface 34 through the similar optical paths as shown in FIG. 4A. By thinning the thickness of the light guide 3B, the optical path length in the light guide 3B may be shortened. Since the thinning of the thickness of the light guide 3B can be achieved with ease in the modification 2, i.e., the optical path length in the light guide 3B can be shortened, the adverse effects due to the absorption of the transparent resin material for the light guide 3B or haze (volume scattering) can be suppressed. In general, the haze may cause volume scattering in a medium, lowering the definiteness at the cut-off line and possibly causing glare light. In particular, the portion near the light incident surface 31 may include a large amount of luminous fluxes, and accordingly, the effect of the shortening the optical path length at that portion may be large. Furthermore, if a polycarbonate resin that is transparent but has high light absorption characteristics, is used for the transparent resin material, the shortening of the optical path near the light incident surface 31 can suppress the lowering the luminous flux.
The attenuation of light can be represented by the following formula:

I=I010−βx 

wherein β is an absorbance, x is a distance that the light passes through a medium, I0 is an intensity of incident light, and I is an intensity of exiting light.
As described above, when compared with the conventional unit, the modification 2 can provide the vehicle lighting unit 1B with a thinner light guide 3B.
Since the reflection region among the reflection regions a1 to a3, b1 to b3, and c1 to c3 can be disposed at a position shifted closer to the light exiting surface 34 as the reflection region is closer to light incident surface 31, the steps d1 to d4 or the like can appear between the adjacent reflection regions as shown in FIGS. 12B and 12C. This can provide a novel appearance to the vehicle lighting unit 1B.
Since the reflection region among the reflection regions a1 to a3, b1 to b3, and c1 to c3 can be disposed at a position shifted closer to the light exiting surface 34 as the reflection region is closer to light incident surface 31, the light internally reflected off the light exiting surface 34 can be prevented from entering the step dl or the like appearing between the adjacent reflection regions.
In the vehicle lighting unit, the plurality of reflection regions a1 to a3, b1 to b3, and c1 to c3 each can form a light distribution pattern part A1 to A3, B1 to B3, or C1 to C3 (see FIG. 15A) constituting a desired light distribution pattern (see FIG. 15B) formed by the light projected through the light exiting surface 34.
With this configuration, when compared with the conventional case in which the reflection surface is a continuous surface (revolved paraboloid), the second reflection surface 33 can be divided into the plurality of reflection regions a1 to a3, b1 to b3, and c1 to c3 each capable of forming a particular light distribution pattern part A1 to A3, B1 to B3, or C1 to C3 as shown in FIG. 15A. This can give a higher degree of freedom for forming the light distribution to the vehicle lighting unit 1B.
In the modification 2, the vehicle lighting unit 1B includes the single light guide 3B, but the presently disclosed subject matter is not limited to this mode. For example, as shown in FIGS. 16A to 16C, two light guides 3B can be arranged with symmetry in the vertical direction, and the light source 12 can be disposed along the optical axis Ax to form the vehicle lighting unit 1C.
<Modification 3>
Next, a description will be given of a modification 3 of the present exemplary embodiment.
FIGS. 17A, 17B, 17C, and 17D are a perspective view when viewed from a front side, a longitudinal cross-sectional view, and a perspective view when viewed from a rear side of a vehicle lighting unit 1D (or modification 3), and a comparative example, respectively.
The vehicle lighting unit 1D of the modification 3 can be configured in the same manner as in the modification 2, except that the light incident surface 31 of the light guide 3C can receive the light and the light source 2 can be disposed to face to the light incident surface 31 so that the light can be internally reflected off a reflection surface 33D corresponding to the second reflection surface 33 and exit through the light exiting surface 34, namely, except that the unit 1D does not include the first reflection surface 32 and the internal reflection is performed once within the light guide 3C by the reflection surface 33D.
Specifically, the light guide 3C can be a solid light guiding lens including the light incident surface 31, the light exiting surface 34, and the reflection surface 33D opposed to the light exiting surface 34 and inclined thereto, so that the light entering through the light incident surface 31 can be internally reflected off the reflection surface 33D and then exit through the light exiting surface 34.
The reflection surface 33D can include a plurality of reflection regions a1 to a3, b1 to b3, and c1 to c3 divided by two horizontal planes and two vertical planes parallel to the optical axis Ax as shown in FIG. 17C.
With reference to FIGS. 17B and 17D, the maximum inscribed circle C3 in FIG. 17B is smaller than the inscribed circle C4 in FIG. 17D, meaning that the thickness of the light guide 3C of the modification 3 is thinner than the light guide with the continuous surface. (The maximum thickness portion of the modification 3 is thinner than that of the above exemplary embodiment.)
In the modification 3, the same advantageous effects can be obtained as in the modification 2.
<Modifications 4 and 5>
Next, modifications 4 and 5 of the present exemplary embodiment will be described with reference to FIGS. 18 to 21. It should be noted that the directions and inclinations are illustrated in these drawings in an exaggerated manner for the convenience of facilitating an understanding of the present disclosure.
FIG. 18 is a longitudinal cross-sectional view of the vehicle lighting unit 1E according to the modification 4. The drawing also illustrates the optical paths as in FIG. 14. The same portions of the vehicle lighting unit lE according to the modification 4 are denoted by the same reference numerals as those in the previous embodiments (modifications).
Modifications 4 and 5 show the case where the second surface 33 can have a plurality of reflection regions being different in reflection direction. Specifically, as illustrated in FIG. 18, the vehicle lighting unit lE according to the modification 4 can be configured such that the reflection regions b1 to b3 can be designed to reflect light slightly lower than the horizontal axis (optical axis) and light reflected off the other reflection regions to form light distribution pattern parts B1 to B3 at much lower positions as illustrated in FIG. 20B.
On the other hand, the vehicle lighting unit 1F according to the modification 5 illustrated in FIG. 19 can be configured such that the reflection regions a1 to a3 can be designed to reflect light slightly lower than the horizontal axis (optical axis) and light reflected off the other reflection regions to form light distribution pattern parts A1 to A3 at much lower positions as illustrated in FIG. 20A than that shown in FIG. 15B.
With this configuration, the light distribution pattern parts can be freely placed at desired areas to form desired light distribution patterns in accordance with specific local regulations or the like. Accordingly, if the lowermost reflection regions c1 to c3 are designed to reflect light slightly lower than the horizontal axis (optical axis) and light reflected off the other reflection regions to form light distribution pattern parts C1 to C3 at much lower positions as illustrated in FIG. 20C.
FIG. 21 is a longitudinal cross-sectional view illustrating the relationship between the optical paths and the first and second reflection portions of the reflection portion of the second surface of the light guide of the vehicle lighting unit 1G according to the presently disclosed subject matter. As illustrated in the drawing, the reflection surface 33 of the second surface can include the first reflection portion (uppermost portions al to a3 in FIGS. 18 and 19) and the second reflection portion (middle portions (b1 to b3) in FIGS. 18 and 19) in order to separately control the direction of the light reflected off these portions. In this configuration, light beams entering the light guide 3 at an uppermost position among the light beams entering the light guide 3 (the uppermost light beam in FIG. 21) can exit through the light exiting portion 34 of the first surface 3a above a reference point RP where light beams exiting the light guide 3 at a lowermost position (the lowermost light beam in FIG. 21) is internally reflected off the internal reflection portion of the first surface 3a. With this configuration, the desired light distribution pattern with a greater freedom of designing the light distribution pattern parts can be obtained with a thinned light guide.
It will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed subject matter without departing from the spirit or scope of the presently disclosed subject matter. Thus, it is intended that the presently disclosed subject matter cover the modifications and variations of the presently disclosed subject matter provided they come within the scope of the appended claims and their equivalents. All related art references described above are hereby incorporated in their entirety by reference.
For example, in the above exemplary embodiment and modifications 2 and 3, the front surface 3a of the light guide 3 can be a flat surface, but may be an appropriate curved surface in accordance with a desired light distribution pattern. For example, as shown in FIG. 9A, the front surface 3a of the light guide 3 can be curved forward (in a convex shape) as in the modification 1, and in this case, as shown in FIG. 9B, a light distribution pattern D1 can be formed horizontally narrower than a light distribution pattern D0 of the light guide with a flat front surface 3a. On the other hand, as shown in FIG. 10A, the front surface 3a of the light guide 3 can be curved rearward (in a concave shape), and in this case, as shown in FIG. 10B, a light distribution pattern D2 can be formed horizontally wider than the light distribution pattern D0 of the light guide with a flat front surface 3a. 
Further, in the exemplary embodiment and the respective modifications, the light guide 3, 3A and the like can be disposed forward and obliquely downward with respect to the light source 2, but the presently disclosed subject matter is not limited thereto. For example, the light guide can be disposed forward and obliquely sideward with respect to the light source 2. In this case the other surfaces can be appropriately designed according to the positional relationship.
The first reflection surface 32 and the light exiting surface 34 can be a single surface 3a (3c), but they can also be formed separately.
Furthermore, the light incident surface 31 of the light guide 3 (3A) can be a curved surface other than a flat surface.

## Claims

1. A vehicle lighting unit having an optical axis, comprising:
a solid light guide having a first surface, a second surface opposite to the first surface and including a reflection portion, and a light incident surface through which light enters the light guide, the first surface including an internal reflection portion and a light exiting portion that are formed as a single continued surface, the light guide configured such that light entering via the light incident surface reaches and is internally reflected off the internal reflection portion of the first surface, is then internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface; and
an LED light source disposed to face forward and obliquely downward with respect to the optical axis and towards the light incident surface, the light source configured to emit light that enters the light guide through the light incident surface, is internally reflected off the internal reflection portion of the first surface, is internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface, wherein
the light is emitted from the LED light source within a predetermined range and enters the light guide through the light incident surface, is internally reflected off the internal reflection portion of the first surface, is internally reflected off the reflection portion of the second surface, and exits through the light exiting portion of the first surface within a predetermined range, and
light entering the light guide at an uppermost position, among the light entering the light guide, exits through the light exiting portion of the first surface above a reference point where light exiting the light guide at a lowermost position is present.

2. The vehicle lighting unit according to claim 1, wherein,
the reflection portion of the second surface includes a plurality of divided reflection regions, and
the reflection regions include at least one reflection region disposed at a reference position and at least one reflection region disposed at a position closer to the light exiting portion of the first surface than the reference position.

3. The vehicle lighting unit according to claim 2, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least one horizontal plane.

4. The vehicle lighting unit according to claim 3, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least one vertical plane.

5. The vehicle lighting unit according to claim 4, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

6. The vehicle lighting unit according to claim 3, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

7. The vehicle lighting unit according to claim 2, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least one vertical plane.

8. The vehicle lighting unit according to claim 7, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

9. The vehicle lighting unit according to claim 2, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

10. The vehicle lighting unit according to claim 2, wherein the plurality of reflection regions are disposed at a position shifted closer to the light exiting portion of the first surface as the reflection region is closer to the light incident surface.

11. The vehicle lighting unit according to claim 2, wherein the plurality of reflection regions each form a light distribution pattern part constituting a desired light distribution pattern formed by the light projected through the light exiting portion of the first surface.

12. The vehicle lighting unit according to claim 2, wherein at least a portion of light rays internally reflected off the plurality of reflection regions of the second surface and projected through the light exiting portion of the first surface are not parallel with, each other, and with, the optical axis.

13. The vehicle lighting unit according to claim 2, wherein at least a portion of light rays internally reflected off the plurality of reflection regions of the second surface and projected through the light exiting portion of the first surface are not parallel with, each other, and, with the optical axis, within a horizontal plane.

14. The vehicle lighting unit according to claim 2, wherein at least a portion of light rays internally reflected off the plurality of reflection regions of the second surface and projected through the light exiting portion of the first surface are not parallel with, each other, and with, the optical axis, within a vertical plane.

15. The vehicle lighting unit according to claim 1, wherein the reflection portion of the second surface is divided into a plurality of reflection regions by at least one horizontal plane.

16. The vehicle lighting unit according to claim 15, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least one vertical plane.

17. The vehicle lighting unit according to claim 16, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

18. The vehicle lighting unit according to claim 15, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

19. The vehicle lighting unit according to claim 15, wherein the plurality of reflection regions are disposed at a position shifted closer to the light exiting portion of the first surface as the reflection region is closer to the light incident surface.

20. The vehicle lighting unit according to claim 15, wherein the plurality of reflection regions each form a light distribution pattern part constituting a desired light distribution pattern formed by the light projected through the light exiting portion of the first surface.

21. The vehicle lighting unit according to claim 1, wherein the reflection portion of the second surface is divided into a plurality of reflection regions by at least one vertical plane.

22. The vehicle lighting unit according to claim 21, wherein the reflection portion of the second surface is divided into the plurality of reflection regions by at least two vertical planes, and
the reflection regions between the two vertical planes are disposed at positions shifted closer to the light exiting portion of the first surface than the adjacent reflection regions on both sides.

23. The vehicle lighting unit according to claim 1, wherein
the reflection portion of the second surface includes at least a first reflection portion and a second reflection portion that are vertically adjacent to each other,
the first reflection portion of the reflection portion of the second surface is configured to reflect light that is projected through the light exiting portion of the first surface at a position above the reference point where light exiting the light guide at the lowermost position is internally reflected off the internal reflection portion of the first surface, and
the second reflection portion of the reflection portion of the second surface is configured to reflect light that is projected through the light exiting portion of the first surface at a position below the reference point where light exiting the light guide at the lowermost position is internally reflected off the internal reflection portion of the first surface, whereby light reflected off the first reflection portion and light reflected off the second reflection portion illuminates different areas.