JP2008021503A - Metal halide lamp for automotive headlamp - Google Patents

Abstract

A conventional metal halide lamp for an automotive headlamp has a drawback in that the emission color changes greatly according to use.
In a metal halide lamp for an automobile headlamp according to the present invention, a metal tube for connecting an external power source, which is welded in a quartz glass made of quartz glass and quartz glass of sealing portions provided at both ends of the arc tube. A foil, a metal halide and a rare earth element halide sealed in the hollow light emitting portion of the arc tube, a pair of refractory metals welded at one end to the metal foil and the other end protruding into the hollow light emitting portion And a coil made of a refractory metal over the electrode in the sealing portion, and the distance L (mm) between the metal foil side end of the coil and the metal foil and the maximum of the metal foil Thickness M (mm) satisfies 40 ≦ L / M and L <1.6.
[Selection] Figure 1

Description

  The present invention relates to a metal halide lamp used for an automobile headlamp.

  In recent years, highly efficient metal halide lamps are being adopted as automobile headlamps. In this metal halide lamp, mercury or a rare gas and a metal halide that emits light of each wavelength are enclosed in a hollow light emitting portion of an arc tube. This metal halide is a compound of a metal and a halogen not contained in rare earth elements such as sodium, scandium, thallium, and indium. The emission color (color temperature) of this metal halide lamp is determined by the type of metal halide and the mixing ratio thereof. In recent years, however, the types and mixing ratios of metal halides have been changed to lanthanides such as dysprosium, neodymium, and thulium, which are widely used in conventional metal halide lamps for general lighting, etc., in response to the diversification of customer needs, particularly emission colors. Some include compounds of rare earth elements and halogens.

  As shown in FIG. 3, a metal halide lamp used in a conventional automobile headlamp has an arc tube 1 made of quartz glass, and an electrode 2 made of tungsten is disposed oppositely in a hollow light emitting portion of the arc tube 1. The electrode 2 is covered with a tungsten coil 3, and a metal foil 4 made of molybdenum is welded to the base end portion of the electrode 2, and the metal foil 4 is welded in quartz glass forming the arc tube 1. Thus, airtightness in the hollow light emitting portion of the arc tube 1 is maintained.

  If the electrode 2 and the quartz glass are welded, a crack (hereinafter referred to as an electrode crack) occurs in the quartz glass due to a difference in thermal expansion between the electrode 2 and the quartz at the time of lighting. In this manner, it is a well-known technique to prevent the electrode 2 and quartz glass from being welded and to prevent electrode cracks by coating the tungsten coil 3 on the electrode 2 portion to which the quartz glass is welded.

Further, with the improvement in performance of the discharge lamp, further improvements have been studied. For example, as shown in Patent Document 1, “a light emitting portion in which electrodes are provided at both ends and a metal halide is sealed inside, and the above-mentioned A metal halide lamp having a tube power of 70 W or less during stable lighting, comprising an arc tube having a sealing tube provided with sealing portions provided at both ends of the light emitting portion, wherein the introduction body connected to the electrode is sealed. In the portion where the electrode is sealed by the sealing portion, at least part of the sealing electrode portion from the boundary between the light emitting portion and the sealing portion to the introduction body is covered with a metal body. When the weight A (mg) of the metal body and the weight of the sealing electrode part B (mg), the relational expression 0.2 ≦ A / B ≦ 1.6 is satisfied. The outer diameter is OD (mm), the light emitting part of the sealing electrode part and the sealing When the length from the boundary to the end of the metal body on the light emitting part side is 1 (mm), the relational expression 0.5 ≦ 1 / OD ≦ 3.5 is satisfied and the outer diameter of the electrode Is a metal halide lamp characterized by satisfying a relational expression of 1.2 ≦ I _la /D≦2.5, where D is (mm) and the tube current during stable lighting is I _la (A). It has been.

  In addition, when the electrode 2 is covered with the coil 3, a slight gap is generated between the hollow light emitting portion and the metal foil 4 through the bonded portion between the quartz and the electrode 2, and the emission color changes when the encapsulated material enters here. Problems arise. An improvement technique has also been proposed for this, for example, as shown in Patent Document 2, in a method of manufacturing a metal halide lamp in which a tungsten coil is attached to an electrode rod and sealed with a quartz glass bulb, the tungsten coil is formed of the electrode rod. The inner diameter is appropriately larger than the outer diameter and is formed as a pitch in which fused quartz glass does not enter between the coil pitches when sealing with the quartz glass bulb. Is welded to the molybdenum foil to which the electrode rod is welded, and then held at approximately half the length of the tungsten coil and pulled to the discharge end side of the electrode rod, whereby the molybdenum of the tungsten coil is pulled. A metal halide lamp is known in which the pitch on the foil side is extended and in close contact with each other. "

Further, “in a metal halide lamp for a headlamp in which a coil is wound around a portion of the electrode provided in the discharge chamber that is in contact with glass to prevent cracks in the sealing portion, the electrode has an electrode diameter d ₀ is set as a range of current density immediately after the start of lighting (9.5 (A / mm ² ) ≦ current density D ≦ 181 (A / mm ² )), and a cross-sectional area S including the electrode and the coil is defined as (S ≦ 0.2 (mm ² )), the inner diameter ID of the coil is set as a range (d ₀ <ID ≦ 1.5 × d ₀ ), and the coil pitch P of the coil is ( P <600%), the interval L between the end of the coil and the metal foil is set as (L ≧ 0.2 mm), and metal halide is (0.3 ± 0.1 mg) in the discharge chamber. and NaI: the ratio of ScI ₃ 4: 1~2: sealing a 1 A metal halide lamp for a headlamp characterized in that the first and second sealing portions extending in the tube axis direction from both ends of the hollow arc tube and the arc tube. A bulb made of quartz glass provided with: a first inner introduction body having a proximal end fixed to the first sealing portion of the bulb, a distal end projecting into the envelope portion of the bulb and having a cathode at the distal end; A second internal introduction body having a side fixed to the second sealing portion of the valve and a tip side protruding into the envelope portion of the valve and having an anode at the tip; and the tip side fixed to the first and second sealing portions And a pair of external lead-in wires whose proximal ends are led out from the first and second sealing portions; and a base of the first internal introduction body that is hermetically embedded in the first sealing portion. A first metal foil for electrically connecting the end and the tip of the external introduction body; A second metal foil that is hermetically embedded in the second sealing portion and electrically connects the proximal end of the second internal introduction body and the distal end of the external introduction body; The cross-sectional area of the metal foil is S _w (mm ² ), the cross-sectional area of the first sealing portion is S _S (mm ² ), the length of the first internal introduction body is L (mm), and the lamp current is I _L (a), when the power consumption of the lamp was W _L (W), the high pressure discharge lamp. "(Patent Document 4), characterized by satisfying equation 1 and equation 2 are also known.
Patent No. 3718077. Japanese Patent No. 3039626. Japanese Patent No. 3218560. Patent No. 3345040.

  However, since the coil is contacted and fused at the location where the metal foil and the electrode are welded in the conventional technology, the gap formed from the hollow light emitting portion of the arc tube to the metal foil is not compared to the case where there is no coil. It was always increasing. Here, when a rare earth element halide contained in a lanthanide system having a high melting point, such as dysprosium, is mainly enclosed in the hollow light emitting part, the electrode and the metal foil weld part are slightly exposed between the electrode and the coil as the light is turned on and off repeatedly. As compared with Na-Sc and the like that have been used conventionally, a large amount of halide invades, and there is a problem that the emission color changes greatly due to the reduction of the inclusions as in the conventional case. This is because the rare earth element halide has a higher melting point than conventional metal halides other than rare earth elements composed of sodium, thallium, indium, etc., so that it easily penetrates into the gap on the low temperature metal foil side, It is estimated that it is difficult to return to the hollow light emitting part.

  Patent Document 3 proposes that the distance L between the metal foil 4 and the metal foil side end of the coil 3 is 0.2 mm or more as a technique for preventing peeling cracks, but in a lamp containing a large amount of rare earth elements, Even if L is 0.2 mm, peeling cracks are generated, and if it is 0.2 mm or more, there are many places where the coil is not covered, so there is a high possibility that electrode cracks will occur, but there is no clarification about this matter .

  On the other hand, in Patent Document 4, as a technique for preventing cracks caused by the difference in thermal expansion between the foil and quartz, the foil cross-sectional area S and the lamp current IL are set to IL / S ≦ 180, that is, the foil cross-section is increased with respect to the current. Although it has been proposed, in metal halide lamps for automobile headlamps, when the thickness of the foil is increased, that is, when the foil cross-sectional area is increased, a phenomenon that peeling cracks are likely to occur is observed.

  Here, as a result of intensive studies to overcome the above-mentioned problems, the present inventors have found that the above L (mm) and the maximum thickness M (mm) of the metal foil satisfy the relationship of 40 ≦ L / M and L <1.6. And found that the above problem can be solved.

  The present invention has been made based on the above findings.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a metal halide lamp that prevents electrode cracks and peeling cracks even when a halide of a rare earth element is enclosed, and that causes little change in emission color during lighting.

  A metal halide lamp for an automotive headlamp according to the present invention includes a light emitting tube made of quartz glass, a metal foil for connecting an external power source welded in quartz glass of sealing portions provided at both ends of the light emitting tube, and the light emitting device. A metal halide and a rare earth element halide sealed in a hollow light emitting portion of a tube, an electrode made of a refractory metal forming a pair with one end welded to the metal foil and the other end protruding into the hollow light emitting portion; It consists of a coil made of a refractory metal over the electrode in the sealing part, and the distance L (mm) between the metal foil side end of the coil and the metal foil and the maximum thickness M (mm) of the metal foil. Satisfies 40 ≦ L / M and L <1.6.

  The metal foil side end portion of the coil is welded to the electrode in the sealing portion, and the other end of the coil is exposed in the hollow light emitting portion.

  The rare earth element halide is 40% or more and 80% or less in a weight ratio with respect to the total amount of halide enclosed in the hollow light emitting portion.

  According to the metal halide lamp for automotive headlamps of the present invention, it is possible to prevent electrode cracks and peeling cracks and to obtain an advantage that the emission color change due to use becomes extremely small.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present invention, as shown in FIGS. 1 to 3, a metal halide lamp having a tube power of 35 W (tube voltage: 85 V, tube current: 0.41 A) is used as the arc tube 1, and the diameter is 0 made of tungsten containing 1% wt of thorium oxide. .25, the base end of the electrode 2 having a total length of 7 mm is connected to a metal foil 4 made of molybdenum having an edge shape at the end, and the free end of the electrode 2 is inserted into the hollow light emitting portion of the arc tube 1 made of quartz glass. Let it protrude. The electrode 2 is coated with a coil 3 made of tungsten, as in the prior art, and mercury, a buffer gas such as xenon gas, and other rare earth elements such as sodium, scandium, thallium, indium, etc. A metal halide which is a compound of a metal and a halogen, and a rare earth element halide which is a compound of a rare earth element and a halogen contained in a lanthanide system such as dysprosium, neodymium, thulium, and the like, the rare earth element halide is The weight ratio is 70% with respect to the total amount of halide sealed in the hollow light emitting part.

  When the maximum thickness of the metal foil 4 is 0.015, 0.020, 0.025 mm, and the L (mm) is changed from 0.4 mm to 1.6 mm in addition to the conventional 0.2 mm. Table 1 shows an experimental example.

  This evaluation was conducted for up to 1500 hours using a test method described in Japan Electric Bulb Industry Association Standard JEL215, and the presence or absence of electrode cracks and peeling cracks and the change in color temperature were confirmed. Considering the headlight white range, the color temperature was good up to 110% of the initial color temperature.

  As is clear from Table 1, peeling cracks occur when L / M is less than 40. This is presumably because the shorter the L, the easier the halide reaches the foil through the coil, and the thicker the M, the larger the holes generated by expansion and contraction, and the easier the halide accumulates.

  On the other hand, when the L / M is less than 40, the change in the color temperature increases by 10% or more from the initial value, and as a result, deviates from the white range. As described above, this is presumably because the emission of mercury became stronger as a result of the halide eroding more of the foil.

  Moreover, since the location where the coil is not covered becomes long when L is 1.6 mm or more, an electrode crack occurs.

  Therefore, when L / M is 40 or more and L is 1.6 mm or less, electrode cracks and peeling cracks can be prevented, and color temperature change can be reduced.

  It is estimated that the thicker the foil, the more the capacity increases, the temperature rise due to the lamp current is mitigated, and the heat release to the external lead is promoted.・ Since the suppression of shrinkage was found to be more effective for peeling cracks, the thinner foil thickness is preferable.

  The thickness M of the foil is preferably 0.015 mm. If the thickness is less than this, the foil is too soft, and it takes man-hours when welding the electrodes and external leads to the foil, and the process of inserting the mount with the electrodes, foil, and external leads into the arc tube, and the accuracy also deteriorates. .

  In this experiment, the rare earth element halide was 70% of the total weight by weight ratio, but other than this (40% or more and 80% or less), the effect of suppressing electrode cracks and peeling cracks was good. However, if it is 80% or more, the luminous efficiency is lowered and the commercial value is lowered, so 80% or less is preferable. Further, if it is 40% or less, the effect of improving the color rendering properties by the rare earth elements becomes thin, so 40% or more is preferable.

  In addition, mercury-free metal halide lamps that do not enclose mercury in the hollow light emitting part do not enclose mercury, so there is no energy loss due to mercury, so rare earth materials with low vapor pressure, such as dysprosium, are more likely to emit light. However, even such mercury-free ones have the same vapor pressure and the like of each metal halide, so that foil cracking due to lighting and emission color change are likely to occur. Therefore, it goes without saying that the present invention can be similarly applied to mercury-free ones.

  As described above, even if the rare earth element halide is encapsulated in a weight ratio of 40% or more and 80% or less, L (mm) and the maximum thickness M (mm) of the metal foil are 40 ≦ L / M and L <1.6. By doing so, it is possible to provide a metal halide lamp which prevents electrode cracks and peeling cracks and has very little change in emission color.

It is a vertical front view of the metal halide lamp for automobile headlamps of the present invention. It is an enlarged view of the principal part of the metal halide lamp for motor vehicle headlamps shown in FIG. It is the sectional view on the AA line of FIG. It is a vertical front view of the conventional metal halide lamp for automobile headlamps.

Explanation of symbols

1 Arc tube 2 Electrode 3 Tungsten coil 4 Metal foil

Claims (3)

  An arc tube made of quartz glass, a metal foil for external power supply welded in the quartz glass of the sealing portion provided at both ends of the arc tube, a metal halide sealed in the hollow light emitting portion of the arc tube, and A rare earth element halide, an electrode made of a refractory metal paired with one end welded to the metal foil and the other end protruding into the hollow light emitting part, and a refractory metal covered with the electrode in the sealing part The distance L (mm) between the metal foil side end of the coil and the metal foil and the maximum thickness M (mm) of the metal foil are 40 ≦ L / M and L <1.6. A metal halide lamp for automobile headlamps characterized by satisfying   2. The front of an automobile according to claim 1, wherein the metal foil side end portion of the coil is welded to the electrode in the sealing portion, and the other end of the coil is exposed in the hollow light emitting portion. Metal halide lamp for lighting.   3. The metal halide lamp for an automotive headlamp according to claim 1, wherein the rare earth element halide is 40% to 80% by weight with respect to the total amount of halide enclosed in the hollow light emitting portion. .

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