Reflector molded of synthetic resin for a lighting device mounted on a vehicle

Abstract: A reflector molded of a synthetic resin for a lighting device mounted on a vehicle is provided, wherein a slit is transversely formed directly below a joint line defined by a reflective surface and an upper flat surface of the reflector with an optical axis as a center in order to minimize or eliminate the undesirable thermal deformation of the reflector when a light source is continuously turned on for a time longer than a predetermined one. Usually, the extent of transverse extension of the slit is determined with the optical axis of the reflector as a center depending on a quantity of electricity consumed by the light source, a distance between the light source and the upper flat surface and an area of the upper flat surface. In case that the reflective surface of the reflector is designed in an asymmetrical configuration, the extent of transverse extension of the slit is determined asymmetrically relative to the optical axis of the reflector corresponding to the degree of asymmetry of the reflective surface.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a lighting device such as a headlight, an auxiliary headlight or the like mounted on a vehicle. More particularly, the present invention relates to improvement of a reflector for the lighting device of the foregoing type. 2. Background Art To facilitate understanding of the present invention, a typical conventional reflector for a lighting device of the foregoing type will be described below with reference to Fig. 3 to Fig. 5. Fig. 3 shows by way of perspective view the structure of a reflector 91 for a lighting device 90 mounted on a vehicle (not shown). The reflector 91 is molded of a synthetic resin and includes a reflective surface 91a having a predetermined configuration composed of, e.g., a revolving parabolic surface, and a light source 92 such as a halogen lamp or the like is disposed at the position substantially coincident with a focus of the reflective surface 91a. In addition, a lens 93 is arranged ahead of the reflector 91 so that the lighting device 90 exhibits desired light distribution properties. For the purpose of adequately coordinating the configuration of the reflector 91 with the design of a vehicle, upper and lower parts of the reflector 91 are cut out to form an upper flat surface 91b and a lower flat surface 91c both of which extend in parallel with an optical axis Z of the lighting device 90. With respect to the lighting device 90 constructed in the above-described manner, it has been found that the light distribution properties immediately after it is turned on vary from the light distribution properties when it is continuously turned on for a predetermined period of time, e.g., ten minutes. This variation of the light distribution properties of the lighting device is exemplified with reference to the light distribution properties employable in case that a light beam is irradiated toward a vehicle running in the opposite direction as illustrated in Fig. 4 and Fig. 5. Specifically, Fig. 4 shows light distribution properties H0 of the lighting device 90 immediately after the light source 92 is turned on, and Fig. 5 shows light distribution properties H1 when the light source 92 is continuously turned on for ten or more minutes. In contrast with the light distribution properties H0, the light beam distribution properties H1 has a separate part H1a which represents that a part of the reflected light beam is slantwise upwardly irradiated by an angle of about 0.6 degrees relative to a horizontal plane H. The appearance of the separate part H1a in that way leads to a problem that a dazzling light beam is generated in the practical use wherein the light source 92 is normally continuously turned on for a certain time. In addition, there arises another problem that visual recognizability of the lighting device 90 is degraded because of undesirable deformation of the contour representing the light distribution properties. To prevent the dazzling light beam from being irradiated from the lighting device 90, it is necessary that when the lighting device 90 is mounted on a vehicle, a controlling unit (not shown) for the lighting device 90 is preliminarily adjusted such that the optical axis of the lighting device 90 is automatically corrected after the light source 92 is continuously turned on for a certain time, e.g., 10 or more minutes, resulting in an idling time being unavoidably required. GB 2 093 580 A discloses a headlamp with an injection molded reflector having a parabolic rear reflecting surface and upper and lower flat surfaces. Directly above the light source, at the hottest point of the upper flat surface, there is provided a C-shaped slit in the upper flat surface in order to avoid the adverse effects of the heat expansion thereof. The slit has, however, the disadvantage that it enables dust and water to enter the headlamp and that the formation thereof requires an injection mold equipped with a sliding structure. SUMMARY OF THE INVENTION The present invention has been made in consideration of the aforementioned background. An object of the present invention is to provide a reflector which is easily molded of a synthetic resin for a lighting device mounted on a vehicle wherein there does not arise a malfunction that a dazzling light beam unpleasant for a driver in another vehicle running in the opposite direction is not irridiated from the lighting device and water and dust do not easily enter the lighting device. The reflector should assure that the undesirable thermal deformation of the reflector caused as a light source is continuously turned on for a long time is minimized or eliminated. The present invention provides a reflector having the features included in claim 1. Preferably the length of said slit is determined with respect to the vertical plane comprising said optical axis of said reflector as a center depending on the quantity of electricity consumed by said light source, the distance between said light source and said upper flat surface, and the area of said upper flat surface. In case that the reflective surface of the reflector is designed in an asymmetrical configuration, the length of the slit extends asymmetrically relative to the vertical plane comprising said optical axis of the reflector corresponding to the asymmetrical configuration of the reflective surface of the reflector. Other objects, features and advantages of the present invention will become apparent from reading of the following description which has been made in conjunction of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated in the following drawings in which: Fig. 1 is a perspective view of a reflector molded of a synthetic resin for a lighting device mounted on a vehicle according to an embodiment of the present invention, particularly showing the structure of the reflector as seen from the rear side; Fig. 2 is a fragmentary sectional view of a reflector shown in Fig. 1, particularly showing in the exaggerated state in which the reflector is thermally deformed as illustrated by phantom lines; Fig. 3 is a perspective view of a conventional reflector or the foregoing type as seen from the rear side; Fig. 4 is a graph which illustrates light distribution properties of the conventional reflector shown in Fig. 3 immediately after a light source is turned on; and Fig. 5 is a graph which illustrates light distribution properties of the conventional reflector shown in Fig. 3 when the light source is continuously turned on for a tim longer than a predetermined one. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail hereinafter with reference to Fig. 1 and Fig. 2 which illustrate a preferred embodiment thereof. Referring to Fig. 1, a lighting device for a vehicle is generally designated by reference numeral 1. The lighting device 1 includes a reflector 2 which is molded of a synthetic resin and constructed according to the embodiment of the present invention. The reflector 2 includes a reflective surface 3 having a predetermined configuration composed of a revolving parabolic plane of which upper and lower end parts are cut out to form an upper flat surface 4 and a lower flat surface 5 extending in parallel with an optical axis Z of the reflector 2, and a light source 6 such as a halogen lamp or the like is disposed at the position substantially coincident with a focus of the reflective surface 3 in the same manner as the conventional lighting device 90 described above with reference to Fig. 3. In addition, a lens (not shown) is arranged ahead of the reflector 2 to provide desired light distribution properties for the lighting device 1. In this embodiment, a slit 7 is transversely formed directly below the intersection line defined by the reflective surface 3 and the upper flat surface 4 while extending in parallel with the intersection line. Basically, the slit 7 is formed through the reflector 2 in the opposite directions by a same length with the optical axis Z as a center. Fig. 2 is a fragmentary sectional view of the lighting device, particularly showing in the exaggerated state in which the reflector 2 is thermally deformed when the light source 6 is continuously turned on for a long time. Specifically, as the light source 6 is continuously turned on, heat is increasingly generated, causing air in the reflector 2 to convectively flow in the upward direction. Since the upper flat surface 4 is located directly above the light source 6, it is largely thermally expanded due to the elevated temperature as represented by phantom lines compared with the other part of the reflector 2 rather than the upper flat surface 4. Thus, a part of the reflective surface 3, especially, the upper part of the same is upwardly deformed, causing the slantwise upward orienting dazzling light beam to be irradiated from the reflective surface 3 with the result that the light distribution properties are undesirably degraded (as illustrated by the separate part H1a in Fig. 5). Incidentally, the other part of the reflector 2 rather than the upper flat surface 4 is uniformly heated at a low rate with a few thermal expansion without any significant effect on the light distribution properties of the lighting device 1. Since the formation of the slit 7 in the above-described manner prevents the large local thermal expansion of the upper flat surface 4 from being conducted to the reflective surface 3, a large part of the reflective surface 3 is not undesirably locally deformed. Thus, there does not arise a malfunction that a dazzling light beam is irradiated from the lighting device 1. With the construction as mentioned above, the length of the slit 7 in the transverse direction is determined with the optical axis Z of the reflector 2 as a center within the range located directly above the light source 6 having an elevated temperature. Since the extent of transverse extension of the slit 7 should be changed depending on a quantity of electricity consumed by the light source 6, a distance between the light source 6 and the upper flat surface 4, and an area or dimensions of the upper flat surface 4, it is preferable that the length of the slit 7 is determined based on the results derived from a variety of experiments. In case that the reflector 2 is designed in the asymmetrical configuration relative to the optical axis Z of the reflector 2 for some reason, there does arise an occasion that the reflective surface 3 is asymmetrically thermally affected by the light source 6 via the upper flat surface 4. For this reason, it is desirable that the extent of transverse extension of the slit 7 is asymmetrically determined with the optical axis Z of the reflector 2 as a center. The slit 7 can easily be formed on the reflector 2 at the same time when the reflector 2 is molded of a synthetic resin, merely by slightly modifying an injection molding die presently employed for injection-molding the reflector 2. Therefore, the number of steps required for producing the lighting device 1 is not increased at all. While the present invention has been described above with respect to a single embodiment thereof, it should of course be understood that the present invention should not be limited only to this embodiment but various change or modification may be made without any departure from the scope of the present invention as defined by the appended claims.

Claims: A reflector (2) molded of a synthetic resin for a lighting device (1) mounted on a vehicle wherein said lighting device (1) includes a light source (6) at the position substantially coincident with the focus of a reflective surface (3) of said reflector (2) having the shape of a paraboloid of revolution of which upper and lower end parts are cut out to form an upper flat surface (4) and a lower flat (5) surface both of which extend in parallel with an optical axis (Z) of said reflector (2), and a slit (7) is provided above the optical axis (Z) and extends to both sides of a vertical plane which comprises the optical axis (Z), characterized in that the slit is transversely formed directly below an intersection line defined by said reflective surface (3) and said upper flat surface (4). The reflector according to claim 1, wherein the length of said slit (7) is determined with respect to the vertical plane comprising said optical axis (Z) of said reflector (2) as a center depending on the quantity of electricity consumed by said light source (6), the distance between said light source (6) and said upper flat surface (4), and the area of said upper flat surface (4). The reflector according to claim 1, wherein the slit (7) extends asymmetrically relative to the vertical plane comprising said optical axis (Z) of said reflector (2) in case of an asymmetrical configuration of said reflective surface (3) of said reflector (2).

Inventors: FURUYA SHIGERU, MATSUZAKI MAKIO, FURUYA, SHIGERU, MATSUZAKI, MAKIO
Applicants: STANLEY ELECTRIC CO LTD, STANLEY ELECTRIC CO., LTD.
Application year: 1993
Main classification: F21M3
IPC codes: F21V15, B60Q1, F21W101, F21V7, F21V14, F21S8, F21V17