JP2000268774A - High pressure discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a psuedo-point optical source configuration in a simple manner by providing an electrode consisting of a composite electrode of a current conductor and a discharge electrode, and specifying the diameter and length of an alumina made cylinder. SOLUTION: A current conductor 3 is formed with a metallization layer 6 provided at the whole side part and a tip end face of a cylindrical core 5 made of polycrystalline alumina simillarly with a discharge lamp 1. Since the core 5 is formed out of the same polycrystalline alumina as the discharge tube 1, the thermal expansion characteristic of the conductor 3 is made substantially equal to that of the tube 1. The length of alumina made cylinder being the tube 1 may be 6 mm or more so that a discharge space of a 1 mm or more arc length can be formed inside, and since an electrode is directly mounted to the tube 1, the diameter of the tube 1 can be made small, 1 mm in diameter experimentally. By connecting and sealing the composite electrode directly to the end of the tube 1 in ths way, a compact high pressure discharge lamp can be provided easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-pressure discharge lamp using a discharge tube made of alumina, and more particularly to a high-pressure discharge lamp which is further miniaturized to be a pseudo point light source.

[0002]

2. Description of the Related Art High pressure discharge lamps using quartz discharge tubes have been widely used as headlights for automobiles because of their advantages such as brightness and high luminous efficiency. In a discharge lamp using such a quartz tube, since the discharge tube is transparent, a light-emitting portion formed by a luminous gas in the discharge tube can be used as a light source of the discharge lamp as it is. It is used as a light source for illumination that requires such a point light source.

[0003]

However, when a high-pressure discharge lamp using a quartz tube has been used for a long period of time, the quartz tube is corroded by corrosive substances such as halides enclosed therein, The devitrification phenomenon appears, concealing the light source part, and it becomes as if the whole quartz tube emits light, which has the problem that it cannot be treated as a point light source, and the luminous flux also decreases. Life as point light source is 20
It was not as long as about 00 hours.

[0004] Therefore, the use of high-pressure discharge lamps for headlamps, which use ceramic discharge tubes made of alumina, which is stable against halides and has a longer life than quartz, has been studied. Since this alumina discharge tube is translucent, when the light emission between the internal discharge electrodes is viewed from the outside of the discharge tube, it is in the same state as the entire discharge tube emits light. Therefore, the entire discharge tube must be viewed as a luminous body, and the entire discharge tube has been reduced to a simulated point light source.

FIG. 6 is an explanatory sectional view showing an example of such a conventional high-pressure discharge lamp. Capillaries 27 are provided at both ends of a discharge tube comprising an alumina cylindrical body 26, and a discharge electrode is provided at the tip thereof. The electrode 29 provided with 28 was inserted and sealed. In the case of this configuration, the entire length L2 can be reduced to about 10 mm and the diameter of the discharge tube D2 can be reduced to about 3 mm, but the structure is complicated and expensive.

In view of the above problems, an object of the present invention is to realize a high-pressure discharge lamp using a small-sized discharge tube made of alumina, which can be used as a pseudo point light source, with a simple configuration.

[0007]

According to a first aspect of the present invention, there is provided a high-pressure discharge lamp according to the first aspect, wherein electrodes are inserted and sealed into openings at both ends of one alumina cylindrical body, and an ionized luminescent material and A high-pressure discharge lamp in which a discharge space filled with a starting gas is formed in the cylindrical body, wherein an electrode is a current conductor in which at least a side surface of a rod-shaped core member made of alumina is coated with a mixture of a metal and a non-conductive material. A composite electrode consisting of a discharge electrode welded to the tip of the conductor or joined by a metal or a mixture of a metal and a non-conductive material;
The alumina cylinder has a diameter of 1 mm to 6 mm and a length of 6 mm to 15 mm.

According to a second aspect of the present invention, in the first aspect, the metal portion of the mixture of the metal and the non-conductive material contains 50% by volume or more of molybdenum, and the non-conductive material portion contains 50% by volume or more of alumina. Be composed.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a high-pressure discharge lamp according to the present invention, in which electrodes 2 are directly inserted into both ends of a discharge tube 1 and a luminescent substance such as a halide or a starting gas is sealed therein. Has been stopped.

The discharge tube 1 is a simple cylindrical body formed of polycrystalline alumina, and the electrode 2 is a substantially cylindrical current conductor 3.
And a discharge electrode 4 provided at the tip thereof. The current conductor 3 is formed by providing a metallized layer 6 on the entire side and the end face of a columnar core material 5 made of polycrystalline alumina, similarly to the discharge tube 1, and the discharge electrode 4 is made of a tungsten bar piece. The end is connected to the current conductor tip surface 3a by welding or metallizing. Reference numeral 7 denotes a lead wire which is metallized on the rear side surface of the current conductor 3.

As described above, by forming the core material of the current conductor 3 from the same polycrystalline alumina as that of the discharge tube 1, the thermal expansion characteristics of the current conductor 3 become almost the same as those of the discharge tube 1, and The adhesion and the sealing properties at both ends of the discharge tube can be kept good over a long period of use. Incidentally, the metallized layer 6 may be formed of a mixture of molybdenum and alumina, and specifically, 50% by volume of molybdenum among the conductive materials in the mixture.
It is preferable that alumina be contained at 50% by volume or more of the non-conductive material portion in the mixture. By doing so, the electrical properties as a current conductor are good, and the adhesion properties with alumina are also good, so that a metallized layer can be favorably formed on the surface of a core material made of alumina.

When a high-pressure discharge lamp using an alumina discharge tube is used for an automobile headlamp, it is convenient to use a pseudo point light source, that is, to reduce the size of the headlight, for example, in designing the reflector as described above. Specifically, it is desired that the discharge tube has a length of 15 mm or less and a diameter of 6 mmφ or less. However, the arc length of the internal discharge part is required to be about 1 mm to 5 mm.

In this respect, in the configuration of FIG.
If the length of the alumina cylindrical body is 6 mm or more, it is possible to form a discharge space with an arc length of 1 mm or more inside. Since the electrodes are directly attached to the discharge tube 1, the diameter of the discharge tube is determined by experiments. It has been confirmed that it can be reduced to 1 mmφ. Therefore, it is possible to easily create a high-pressure discharge lamp that is a pseudo point light source using the high-pressure discharge lamp having the above-described configuration. The minimum value of the discharge tube diameter is determined by the tube wall load at the time of operation of the lamp. The tube wall load useful as a high-pressure discharge lamp is at least 15 lumen / cm ² . It has been confirmed by experiments that the diameter of the cylindrical body needs to be 1 mmφ (wall thickness: 0.25 mm) or more.

FIG. 2 shows a method of fixing and sealing the electrodes, wherein (a)
Provides a small gap between the cylindrical body opening 1a and the current conductor 3, and seals the gap using a known sealing frit 9;
This shows a sealed state. (B) shows a state in which the metallized layer 10 is also formed on the end of the cylindrical body, and the metallized layer 6 formed on the side of the current conductor is tightly sealed by laser welding. The electrodes at both ends of the discharge tube may be sealed by different methods by combining the above methods. Thus, by connecting the composite electrode directly to the end of the discharge tube and sealing it without providing a capillary, a simple structure can be obtained, and a small high-pressure discharge lamp can be easily produced.

FIG. 3 shows another shape of the discharge electrode.
Is a molybdenum ring 1 at the base end of the tungsten rod 12.
3 and the current conductor 3 together with the molybdenum ring 13.
Are joined by metallization or welding.
(B) shows a shape in which a skirt portion 14a having an enlarged diameter is provided at the base end portion of the tungsten rod 14 to increase the bonding area. 3C, the base end of the tungsten rod 15 is welded to a molybdenum plate 16 and the molybdenum plate is metallized to the current conductor 3. And
4D, the base end of the tungsten rod 17 is bent, and a ring 17a is provided to increase the bonding area, and is connected to the current conductor. In this manner, by increasing the area of the current conductor connection portion of the discharge electrode, it is possible to make a good connection even when the tip connection surface of the current conductor is flat.

FIG. 4 shows a connection form between the current conductor and the discharge electrode. FIG. 4A shows a state in which a concave portion 21 is provided at the distal end of the current conductor 20 and the base end of the discharge electrode 4 is buried and metallized or welded. ing. 2B, the tip of the current conductor 23 is formed as an inclined surface 24, and the base of the discharge electrode is also formed as an inclined surface 25.
Is formed, and the contact area is enlarged to form a metallized or welded joint. In this way, the shape of the tip end of the current conductor may be devised to increase the bonding strength with the discharge electrode to obtain a good bonding.

Although the discharge tube has a simple cylindrical shape in the above embodiment, it may have a shape with a bulge at the center as shown in FIG. Further, as shown in FIG. 4, the current conductor may be provided with a metallized layer on the entire surface of the alumina core material. Furthermore, the discharge tube made of alumina can mask the light emitting surface by providing a metallized layer on the side surface, so that the control of the radiation direction can be easily performed, and the masking portion can be easily formed by vapor deposition or the like. Can be formed. Further, in the above-described embodiment, the description has been given on the assumption that the high-pressure discharge lamp is a pseudo point light source. It is also possible to use it as a light source.

[0018]

As described above in detail, the high pressure discharge lamp according to the first aspect of the present invention has a simple structure in which electrodes are inserted and sealed at both ends of one alumina cylindrical body. The process can be simplified, the size can be easily reduced, and if used as a headlight for an automobile, a highly efficient and long-life light source can be obtained. In addition, since the current conductor has the same core material made of the same alumina as the discharge tube, the thermal expansion characteristics of the current conductor are almost the same as the thermal expansion characteristics of the discharge tube, and the sealing characteristics of the electrodes can be used for a long time. It can be kept good throughout.

According to the high pressure discharge lamp according to the second aspect of the present invention, in addition to the effect of the first aspect, even when an alumina core is used for the current conductor, the electrical characteristics of the metallized layer formed on the surface thereof In addition, the adhesive property with the core material can be made good, and good properties as a current conductor can be maintained.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a high-pressure discharge lamp showing an example of an embodiment of the present invention.

FIGS. 2A and 2B show a method of fixing and sealing the electrode of FIG. 1, wherein FIG. 2A is a cross-sectional explanatory view of sealing with a frit seal, and FIG.

3A and 3B show other shapes of a discharge electrode connecting portion, wherein FIG. 3A shows a configuration in which a molybdenum ring is provided, FIG.
(C) is a cross-sectional view showing a form in which a molybdenum plate is provided, and (d) is a cross-sectional view showing a form in which a ring is formed.

FIG. 4 is a cross-sectional view showing another form of a current conductor tip.
(A) is a diagram in which a concave portion is provided, and (b) is a diagram in which an inclined surface is provided.

FIG. 5 is an explanatory sectional view showing another embodiment of the high-pressure discharge lamp of the present invention.

FIG. 6 is an explanatory sectional view of a high-pressure discharge lamp using a conventional alumina discharge tube.

[Explanation of symbols]

1. discharge tube, 2. electrode, 3. current conductor, 4. discharge electrode, 5. core material, 6, 10 metallized layer.

Claims (2)

[Claims] 1. A high-pressure discharge lamp in which electrodes are respectively inserted and sealed into openings at both ends of one alumina cylindrical body, and a discharge space filled with an ionized luminescent substance and a starting gas is formed in the cylindrical body. An electrode is a current conductor in which a mixture of a metal and a non-conductive material is coated on at least a side surface of an alumina rod-shaped core material, and is welded to the tip of the current conductor or joined by a metal or a mixture of a metal and a non-conductive material. Electrode comprising a discharge electrode having a diameter of 1 mmφ to 6 mmφ and a length of 6 mm to 15 m.
m, a high-pressure discharge lamp. 2. A metal portion of a mixture of a metal and a non-conductive material contains at least 50% by volume of at least one of molybdenum and tungsten, and a non-conductive material portion contains 50% or more of alumina.
The high-pressure discharge lamp according to claim 1, which contains at least volume%.