Discharge lamp for an automotive vehicle

Abstract: In the conventional discharge lamp for an automotive vehicle, since an optical distortion is generated in an arc shape at a time of passing through a discharge chamber portion and a shining portion is generated in a seal portion, a light distribution is not suitably controlled at a time of assembling a light equipment, so that there is a problem that a formation of the light distribution becomes difficult. In accordance with a discharge lamp (1) for an automotive vehicle of the present invention, a taper portion (22a) is provided in a seal portion (22), a discharge chamber portion (21) is structured such that a curvature of a tube wall in a region of an angle 45 degrees to both sides from a plane X perpendicular to a tube axis Z as seen from a position of a center P of the discharge chamber portion (21) is substantially constant, a ratio of a thickness of the tube wall within the above range is set to be a value within a range from 1 to 0.8, and a discharge bulb (2) and an outer cover tube (6) are in contact with each other in the lowermost portion of the discharge chamber portion (21), the other portion than the arc portion is prevented from shining in the taper portion provided in the seal portion, by specifying the shape of the discharge chamber portion, an optical distortion at a time of passing through the discharge bulb can be reduced, and by bringing the discharge bulb and the outer cover tube into contact with each other, a non-evaporated metal halide material can be stored in the narrow range.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp and particularly to a structure of a discharge lamp suitable for using a light source for a lighting equipment such as a head lamp, a fog lamp and the like for an automotive vehicle. 2. Background Art An embodiment of a structure of a conventional discharge lamp 90 for an automotive vehicle is shown in Figs. 4 and 5. At first, the discharge lamp 90 for an automotive vehicle is constituted by a discharge bulb 91, an outer cover tube 95 and a socket 96 for mounting to a lighting device for an automotive vehicle (not shown). In this case, Fig. 4 shows a cross section in a vertical direction with respect to a state of mounting the discharge lamp 90 for the automotive vehicle to the automotive vehicle, and Fig. 5 shows a cross section in a horizontal direction with respect to the mounting structure to the automotive vehicle. In this case, the discharge bulb 91 comprises a discharge chamber portion 91a and a seal portion 91b, as shown in Fig. 5. The discharge chamber portion 91a has a contour of a substantially spherical shape or a substantially cylindrical shape and is provided with a space for being discharged therewithin. On the contrary, the seal portion 91b is provided with discharge electrodes 92, a molybdenum foil 93 and a lead wire 94. The discharge electrodes 92 are held in an opposing manner within the discharge chamber portion 91a with a suitable interval and an electric power can be supplied to the discharge electrode 92 from an outer portion. Since the discharge bulb 91 is covered by the outer cover tube 95 (refer to Fig. 4), the discharge bulb 91 is prevented from being cooled by the open air and the like so as not to maintain a suitable temperature, thereby preventing a reduction of luminous efficiency. In most cases, a shield film 95a for shielding a portion which generates a harmful light such as a dazzling light and the like at a time of assembling the discharge lamp 90 for the automotive vehicle to the light equipment for the automotive vehicle is provided on the surface of the outer cover tube 95. When the electric power is supplied to the discharge lamp 90 for the automotive vehicle having the above structure, the discharging is performed between the discharge electrodes 92, so that a noble gas such as a xenon gas and the like and a metal halide such as a scandium and the like sealed within the discharge chamber portion 91a emit light. Accordingly, for example, a white light having a color temperature near 4800 °K is emitted and for example, an excellent color rendering property in comparison with a light having a color temperature near 2800 °K of a filament type such as a halide electric lamp and the like can be obtained. However, in the conventional discharge lamp 90 mentioned above, since at first, a non-evaporated metal halide H is attached to a lower portion in a mounting state within the discharge chamber portion 91a around a relatively wide area (refer to Fig. 4), a light passing through the portion from an arc K, that is, a downward light generates coloration and diffusion. In this case, generally, since the light is vertically and laterally inverted after assembled in the lamp equipment for the automotive vehicle and reflected in a reflecting mirror, the downward light passing through the non-evaporated metal halide mentioned above is converted to the upward light so as to be the dazzling light. In order to avoid this problem, a light distribution characteristic of the light equipment is generally made downward, however, in this case, the light can not reach far, so that there is a problem that a far visibility is reduced. Further, secondly, when the seal portion 90b is formed in the conventional discharge lamp 90 for the automotive vehicle, only heating and pressing are performed and the shape of the seal portion 91b obtained thereby is not controlled, so that the curvature suddenly changes at a connecting portion 91c with respect to the discharge chamber portion 91a, and a shining light spot L is generated near the portion, so that a state as if a plurality of light source exist is made (refer to Fig. 5). Accordingly, there occurs a problem that it is difficult to form the light distribution characteristic as the light equipment for the automotive vehicle. Still further, thirdly, the shape of the discharge chamber portion 91a is not sufficiently considered in an optical view, for example, in most cases, the thickness is suddenly changed at a portion near the seal portion 91b of the discharge chamber portion 91a, so that the light passing through the portion from the arc K receives an optical distortion such as a refraction and a change of shape. Accordingly, there occurs a problem that it is difficult to form the light distribution characteristic in the same manner as that mentioned above. Accordingly, an object of the present invention is to solve the above problems. SUMMARY OF THE INVENTION In order to solve the above conventional problems, in accordance with the present invention, there is provided a discharge lamp for an automotive vehicle comprising a discharge bulb comprising a discharge chamber portion forming a discharge space and a pair of seal portions for sealing both ends of said discharge chamber portion, respectively, said discharge bulb being generally spherically or cylindrically shaped defining a tube axis connecting the seal portions, said seal portion holding a pair of discharge electrodes in a way that they are opposed to each other, an outer cover tube covering said discharge bulb with a taper portion being provided at an end of each said seal portion adjacent to the discharge chamber portion being narrowest near the discharge chamber portion, said taper portion defines an angle with respect to the tube axis of said discharge bulb equal to or less than 45 degrees, a curvature of a tube wall of said discharge chamber portion, in a cross section thereof along said tube axis within a range of 45 degrees on both sides of a plane perpendicular to said tube axis at a central position of the discharge chamber portion, is substantially constant, a ratio of the minimum value with respect to the maximum value of a thickness of the tube wall measured within said range is between 1 and 0,8, said discharge bulb and said outer cover tube are in contact, with the portion of said discharge chamber portion having the maximum outer diameter being in contact with said outer cover tube, in the lowermost portion of the discharge chamber portion in a use state of the discharge lamp defined by a generally horizontal arrangement of the tube axis. BRIEF DESCRIPTION OF THE DRAWINGS These objects and advantages of the present invention will become clear from the following description with reference to the accompanying drawings, wherein: Fig. 1 is a cross sectional view in a horizontal cross section in a state of mounting to an automotive vehicle which shows a main part of an embodiment of a discharge lamp for an automotive vehicle in accordance with the present invention; Fig. 2 is a cross sectional view in a vertical cross section in a state of mounting to the automotive vehicle which shows the same embodiment; Fig. 3 is a cross sectional view which shows a main part of another embodiment of the discharge lamp for the automotive vehicle in accordance with the present invention; Fig. 4 is a cross sectional view which shows a conventional embodiment; and Fig. 5 is a cross sectional view which shows a main portion of the conventional embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in accordance with the present invention will be explained in detail below with reference to the accompanying drawings. Fig. 1 shows a discharge bulb 2 of a discharge lamp 1 for an automotive vehicle in accordance with the present invention, and shows a horizontal cross section in a state of mounting to the automotive vehicle. In the present invention, the discharge bulb 2 is formed by a discharge chamber portion 21 and a pair of seal portions 22 provided in both ends thereof. The seal portion 22 is provided with a discharge electrode 3, a molybdenum foil 4 and a lead wire 5 in the same manner as that of the conventional one. In accordance with the present invention, the shape of the discharge chamber portion 21 and the seal portion 22 is defined. At first, the seal portion 22 is provided with a taper portion 22a which has a narrow portion in the discharge chamber portion 21 end and an angle α with respect to a tube axis Z of the discharge bulb 2 equal to or less than 45 degrees (preferably equal to or less than 20 degrees) in a portion close to the discharge chamber portion 21 of each of the seal portion 22. In forming the taper portion 22a, in the conventional method, the corresponding portion is held between the metal molds and the like from both directions in a state of being heated so as to be softened. Since the shape after crushed has not been controlled, the metal mold is formed to a suitable shape, thereby forming so as to make the shape at a time of being crushed constant. At this time, the taper portion 22a is provided for the purpose of preventing a sudden change of the curvature from generating in a connecting portion 23 between the discharge chamber portion 21 and the seal portion 22, thereby preventing the portion from shining. Accordingly, in the conventional embodiment, with respect to the crushing direction in which the sudden change of the curvature is not generated, that is, the vertical cross sectional direction in a state of mounting to the automotive vehicle shown in Fig. 2, the formation of the taper portion may be omitted. Further, in accordance with the present invention, with respect to the discharge chamber portion 21, by specifying the curvature and the thickness, an optical distortion which is received at a time when the light from the ark K passes through the discharge chamber portion 21 is reduced. In this case, as a result of the measurement by the inventor for achieving the present invention, it is ascertained that the discharge of the light in this type of discharge lamp 1 for the automotive vehicle is concentrated in a range in which both angle β with respect to a plane X perpendicular to the tube axis Z as seen from the position of the center P of the discharge chamber portion 21 becomes 45 degrees. Accordingly, the specification of the shape in the discharge chamber portion 21 can be limited to the range of the angle β mentioned above, so that the present invention makes the curvature of the cross section coinciding with the tube axis Z of the tube wall in the range substantially constant or with no curvature, that is, close to a circular arc shape or a linear shape in both an inner surface 21a and an outer surface 21b, thereby passing through in a constant condition. In addition to this, a ratio of the minimum value of the thickness of the tube wall measured in a direction as seen from the position of the center P within the above range with respect to the maximum value thereof is set to be a range from 1 to 0.8. In this case, the position showing the maximum value of the thickness of the tube wall may coincide with the plane X perpendicular to the tube axis Z, or may coincide with the position forming 45 degree with respect to the plane X. In either case, it is sufficient if the ratio between the both values is within the range mentioned above. By constituting in the above manner, the discharge bulb 2 does not shine at a portion other than the ark K in the seal portion 22, and is hard to receive the optical distortion such as the enlargement, compression or curvature at a time when the light from the ark K passes through in the discharge chamber portion 21. Further, in addition to the above, the present invention can reduce the influence due to the non-evaporated metal halide material H, which is achieved by bringing the discharge bulb 2 into contact with the outer cover tube 6 at a predetermined position as shown in Fig. 2. In the drawing, reference numeral 7 denotes a socket. Fig. 2 shows the discharge lamp 1 for the automotive vehicle 1 by a vertical cross section in the mounting state to the automotive vehicle, in which the discharge bulb 2 and the outer cover tube 6 are in contact with each other in the lower portion and the place bringing both parts into contact with each other is the lowermost end of the discharge bulb 2, that is, the portion in which the outer diameter of the discharge chamber portion 21 becomes maximum. By structuring in the above manner, the portion being in contact with the outer cover tube 6 of the discharge chamber portion 21 radiates the heat to the open air through the outer cover tube 6 so that is kept in a relatively low temperature with respect to the other portions of the discharge chamber portion 21. Accordingly, the non-evaporated metal halide material H stocked in the portion having the low temperature is stored in the narrow range concentrated to the portion close to the place being in contact therewith. Accordingly, the rate of the light in which the coloration and diffusion are performed is reduced, thereby reducing the influence thereof. Here, in accordance with the trial manufacture and the experiment by the inventor, when the metal halide material H is stored in the narrow region within the discharge chamber portion 21 as mentioned above, it is ascertained that the shape and the size of the discharge chamber portion 21 relates thereto. Accordingly, as shown in Fig. 3, by setting the thickness of the tube wall of the discharge chamber portion 21 close to the seal portion 22 thinner than the thickness of the tube wall of the center portion of the discharge chamber portion 21, the thinner portion becomes higher temperature, so that the metal halide material H further concentrates to the center portion and is stored. The above matter will be mentioned below by concrete values. When the thickness of the discharge chamber portion 21 crossing to a plane Y passing through the front end of the discharge electrode 3 and perpendicular to the tube axis Z is set to be A, the thickness of the discharge chamber portion 22 crossing to the plane X passing through the center P of the discharge chamber portion 21 and perpendicular to the tube axis Z is set to be B, and B/A ≥ 1.15, it is ascertained that the concentration of the metal material H can be further achieved. In this case, when the thickness A is set to be a value less than 0,8 mm, the mechanical strength of the discharge chamber portion 21 becomes insufficient, so that the thickness A is limited to be a value equal to or more than 0,8 mm. Here, in accordance with the trial manufacture by the inventor when the above conditions are given to the discharge chamber portion 22, the range of the metal halide material H stored in the discharge chamber portion 22 at a time of lighting becomes narrower than the distance between both the opposing discharge electrodes 3 (about 2/3), so that influence with respect to the passing light due to the coloration and diffusion can be further reduced. As mentioned above, in accordance with the discharge lamp for the automotive vehicle of the present invention, since the taper portion is provided in the portion of each of the seal portion close to the discharge chamber portion, the discharge chamber portion is structured such that the curvature of the tube wall in the region of the angle 45 degrees to both sides from the plane perpendicular to the tube axis as seen from the position of the center of the discharge chamber portion is substantially constant, the ratio of the minimum value of the thickness of the tube wall within the above range with respect to the maximum value thereof is set to be a value within the range from 1 to 0.8, and the discharge bulb and the outer cover tube are in contact with each other at the portion having the maximum outer diameter of the discharge chamber portion in the lowermost portion in the use state, the other portion than the arc portion is prevented from shining in the taper portion provided in the seal portion, by specifying the shape of the discharge chamber portion, the optical distortion when the light from the arc passes through the discharge bulb can be reduced, and by bringing the discharge bulb and the outer cover tube into contact with each other, the non-evaporated metal halide material can be stored in the narrow range. Accordingly, the light distribution of the discharge lamp for the automotive vehicle of this type can be improved.

Claims: A discharge lamp for an automotive vehicle comprising : a socket (7), a discharge bulb (2) with a substantially spherical shape or substantially cylindrical shape, said discharge bulb being constituted by a discharge chamber portion (21) forming a discharge space and a pair of seal portions (22) for sealing both ends of said discharge chamber portion (21), respectively, said seal portions (22) holding a pair of discharge electrodes (3) in such a manner that they are opposed to each other for forming a discharge within said discharge space and an outer cover tube (6) covering said discharge bulb (2), characterized in that a taper portion (22a) is provided at an end of each said seal portion (22) adjacent to the discharge chamber portion (21), said taper portion being narrow near the discharge chamber portion (21), and defining an angle (α) with respect to a tube axis (Z) of said discharge bulb (2) equal to or less than 45 degrees, that a curvature of a tube wall of said discharge chamber portion (21), in a cross section thereof in a plane containing the tube axis (Z), is substantially constant within a range of 45 degrees on both sides of a plane (X) perpendicular to said tube axis (Z) and containing a central position (P) of the discharge chamber portion (21); that a ratio of the minimum value with respect to the maximum value of a thickness of the tube wall measured within said range is between 1 and 0, 8; that said discharge bulb (2) and said outer cover tube (6) are in contact, that the portion of said discharge chamber portion (21) having the maximum outer diameter is in contact with said outer cover tube (6), and that said discharge bulb (2) is positioned with respect to the socket (7) so that in a use state of the discharge lamp the contact between the discharge chamber portion (21) and the outer cover tube (6) is the lowermost portion of the discharge bulb (2). A discharge lamp for an automotive vehicle as recited in claim 1, wherein when a thickness of said discharge chamber portion (21) crossing to a plane (Y) passing through the front end of said discharge electrode (3) and perpendicular to said tube axis (Z) is set to be A and a thickness of said discharge chamber portion (21) crossing to a plane (X) passing through the center (P) of said discharge chamber portion (21) and perpendicular to said tube axis (Z) is set to be B, relations A ≥ 0,8 mm and B/A ≥ 1,15 are effected.

Inventors: FUTAMI TAKASHI, MUTO MASAAKI, OMORI SHINYA, YAGUCHI YASUHISA, FUTAMI, TAKASHI, MUTO, MASAAKI, OMORI, SHINYA, YAGUCHI, YASUHISA
Applicants: STANLEY ELECTRIC CO LTD, STANLEY ELECTRIC CO., LTD.
Application year: 1998
Main classification: H01J61
IPC codes: H01J61