JP2008262855A - Metal halide lamp for automobile headlamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal halide lamp for an automobile headlamp capable of keeping an excellent life characteristic by suppressing white turbidity. <P>SOLUTION: This metal halide lamp for an automobile headlamp is provided with: an airtight vessel 1 having a discharge part 11 having a discharge space 14 formed inside, and a pair of sealing parts 12a and 12b formed at both ends of the discharge part 11; xenon and a metal halide 2 filled in the discharge space 14; and a pair of straight rod-like electrodes 3a2 and 3b2 having one-side ends sealed to the sealing parts 12a and 12b, and the other-side ends arranged oppositely to each other in the discharge space 14, and having a diameter R (mm) satisfying 0.32≤R≤0.40; and is lit by being supplied, in startup, with power almost twice or more as much as that in a stable period, with a tube axis arranged horizontally. In the metal halide lamp, filling pressure of xenon is not smaller than 13 atm; mercury is not essentially included; and, when it is defined that a maximum current value immediately after startup is I<SB>SMAX</SB>(A), I<SB>SMAX</SB>/R (A/mm) satisfies a relationship of 7.5≤I<SB>SMAX</SB>/R≤9.4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal halide lamp for an automotive headlamp that is lit in a substantially horizontal state.

  A metal halide lamp used for an automobile headlamp that is lit in a substantially horizontal state is disclosed in Japanese Patent Laid-Open No. 2001-6610 (hereinafter, Patent Document 1), Japanese Patent Laid-Open No. 2003-173663 (hereinafter, Patent Document 2), and the like. Are known. This metal halide lamp is a so-called mercury-free lamp in which xenon and a metal halide are enclosed as a discharge medium and mercury is not enclosed. Since this mercury-free lamp tends to be less bright than conventional mercury-containing lamps, attempts have been made to enclose high-pressure xenon in the discharge space in order to increase the total luminous flux.

Japanese Patent Laid-Open No. 2001-6610 JP 2003-173663 A

  However, in a mercury-free lamp in which xenon is sealed at a high pressure, there is a problem that the luminous flux during the lifetime is rapidly reduced. This problem was found to be particularly serious when the xenon sealing pressure was 13 atm or higher.

  As a result of various investigations by the inventor regarding this problem, it was found that this was caused by white turbidity occurring when high power was applied immediately after starting. In other words, metal halide lamps used in automobile headlamps require that the luminous flux rise immediately after the start of lighting, and therefore, higher power is supplied than when it is stable immediately after starting. I have discovered that this problem occurs. Therefore, as a result of further investigation, it was found that by controlling the current value flowing through the electrode immediately after start-up, white turbidity can be suppressed even when xenon is sealed at a high pressure, and the life characteristics can be kept good. It came to do.

  An object of the present invention is to provide a metal halide lamp for an automotive headlamp that can suppress white turbidity and maintain good life characteristics.

In order to achieve the above object, a metal halide lamp for an automotive headlamp according to the present invention includes a discharge part in which a discharge space is formed, and an airtight container having a pair of sealing parts formed at both ends of the discharge part. A discharge medium containing xenon and a metal halide enclosed in the discharge space; a pair of electrodes having one end sealed to the sealing portion and the other end opposed to the discharge space; In a metal halide lamp for automotive headlamps, in which the shaft is arranged substantially horizontally and power is supplied at about twice or more than when it is stable at start-up, the enclosed pressure of xenon in the discharge medium is 13 atm or more. In addition, mercury is essentially not contained, and when the maximum current value immediately after starting is I _SMAX (A) and the diameter of the electrode is R (mm), I _SMAX / R (A / mm) is 7 .5 ≦ _{I SM} Characterized by satisfying the relationship _X /R≦9.4.

  According to the present invention, white turbidity can be suppressed and good life characteristics can be maintained.

(First embodiment)
Hereinafter, a metal halide lamp for an automobile headlamp which is an embodiment of a metal halide lamp for an automobile headlamp according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a first embodiment of a metal halide lamp for an automobile headlamp according to the present invention.

  A metal halide lamp used for an automobile headlamp has an airtight container 1 as a main part. The hermetic container 1 has an elongated shape in the lamp axis direction, and a substantially elliptical discharge portion 11 is formed at a substantially central portion thereof. Plate-shaped sealing portions 12a and 12b are formed at both ends of the discharge portion 11, and cylindrical non-sealing portions 13a and 13b are formed at both ends thereof. The airtight container 1 can be formed of a material having heat resistance and translucency, such as quartz glass.

Inside the discharge part 11, a discharge space 14 having a substantially cylindrical shape at the center and tapered at both ends is formed in the axial direction. The volume of the discharge space 14 as is vehicle ^headlights, is preferably a 10mm ³ ~40mm 3.

The discharge space 14 is filled with a discharge medium composed of the metal halide 2 and a rare gas. The metal halide 2 is composed of sodium iodide (NaI), scandium iodide (ScI ₃ ), zinc iodide (ZnI ₂ ), and indium bromide (InBr). In addition, about the halogen couple | bonded with metal halides other than a scandium iodide, it is not limited to the above, You may use it combining a bromine, chlorine, or several halogen.

  As the rare gas, xenon which has high luminous efficiency immediately after starting and mainly acts as a starting gas is enclosed. Since the xenon sealing pressure increases with increasing brightness, it is sealed at 13 atm or more. There is no particular upper limit, but at present, about 20 atm is considered the enclosure limit. The pressure of xenon is measured by collecting and surveying xenon in the discharge space 14 by breaking the boundary between the discharge part 11 and the sealing part 12a (or the sealing part 12b) in water, and then measuring the internal volume of the discharge part 11 Can be calculated by measuring.

  Here, the discharge space 14 essentially does not contain mercury. This “essentially mercury-free” means that it contains no mercury at all, or an amount equivalent to almost no encapsulation even when compared with a conventional metal halide lamp containing mercury, for example, less than 2 mg per ml, Preferably, even if an amount of mercury of 1 mg or less is present, it is acceptable.

Mounts 3a and 3b are sealed inside the sealing portions 12a and 12b.
The mounts 3a and 3b are configured by integrally forming metal foils 3a1 and 3b1, electrodes 3a2 and 3b2, coils 3a3 and 3b3, and external lead wires 3a4 and 3b4.

  Metal foil 3a1, 3b1, for example, a thin metal plate made of molybdenum.

  The electrodes 3a2, 3b2 are tritated tungsten electrodes obtained by doping tungsten with thorium oxide. The base end side is connected to the end of the metal foil 3a1, 3b1 on the discharge part 11 side by laser welding. On the other hand, the tip side is arranged so that the tips of each other face each other while maintaining a predetermined distance between the electrodes in the discharge space 14. Here, it is desirable that the predetermined inter-electrode distance is about 4.2 mm in terms of appearance, that is, not the actual distance but the appearance of the lamp. The diameter R of the electrodes 3a2, 3b2 is preferably 0.32 mm to 0.40 mm. The electrodes 3a2, 3b2 are preferably in the shape of a straight bar as in the present embodiment.

  The coils 3a3 and 3b3 are made of, for example, doped tungsten, and are spirally wound around the shafts of the electrodes 3a2 and 3b2 sealed by the sealing portions 12a and 12b. However, the coils 3a3 and 3b3 are not wound around the shaft portions of the electrodes 3a2 and 3b2 connected to the metal foils 3a1 and 3b1, but are wound in the direction of the discharge space 14 from the end of the foil.

  The external lead wires 3a4 and 3b4 are made of, for example, molybdenum, and are connected to end portions of the metal foils 3a1 and 3b1 on the opposite side to the discharge portion 11 by welding or the like. The other end sides of the external lead wires 3a4 and 3b4 extend along the tube axis to the outside of the sealing portions 12a and 12b, and further extend in the outward direction while being positioned at the approximate center of the non-sealing portions 13a and 13b. ing. One end of an L-shaped support wire 3c made of nickel is connected to the lead wire 3b4 extending to the front end side. The other end of the support wire 3c extends in the direction of a socket 6 described later. The support wire 3c parallel to the tube axis is covered with a sleeve 4 made of ceramic.

  A cylindrical outer tube 5 having an action of blocking ultraviolet rays by adding an oxide such as titanium, cerium, or aluminum to quartz glass is provided outside the hermetic container 1 configured as described above. Along the airtight container 1, the airtight container 1 is provided concentrically. These connections are made by melting the cylindrical non-sealing portions 13a, 13b at both ends of the hermetic container 1 and both ends of the outer tube 5. That is, welded portions 51 a and 51 b are formed at both ends of the airtight container 1 and the outer tube 5. In the space between the airtight container 1 and the outer tube 5, for example, a rare gas such as nitrogen, neon, argon, xenon, or the like can be sealed or mixed.

  And the socket 6 is connected to the non-sealing part 13a side of the outer tube 5 in a state of covering the airtight container 1 inside. For these connections, the metal band 71 attached to the outer peripheral surface of the outer tube 5 in the vicinity of the non-sealed portion 13a is connected to four metal tongue pieces formed on the opening end of the socket 6 on the airtight container 1 holding side. 72 (two are shown in FIG. 1). In order to further strengthen the connection, the contact points of the metal band 71 and the tongue piece 72 are welded by laser. Note that a bottom terminal 8a and a side terminal 8b are formed at the bottom of the socket 6, and a lead wire 3a4 and a support wire 3c are connected thereto, respectively.

  When a lighting circuit is connected to the bottom terminal 8a and the side terminal 8b of the lamp configured as described above and power is turned on, an arc 9 is formed between the electrodes, and a lighting state is obtained. In that case, in the metal halide lamp used for a motor vehicle headlamp, the tube axis | shaft of a lamp | ramp is arrange | positioned so that it may become substantially horizontal on the use. “The tube axis is substantially horizontal” means a state in which the arc 9 formed during lighting is horizontally arranged to be curved upward due to the influence of buoyancy and convection. Note that the lamp lighting power is set to about 75 W, which is more than twice that at the start, while it is about 35 W at the start as shown in FIG. .

Here, the metal halide lamp of the present invention, in order to solve the problem, when the maximum current value immediately after the start _{I SMAX} (A), the diameter of the electrode 3a2,3b2 was _{R (mm), I SMAX /} R It is lit so that (A / mm) satisfies the relationship of 7.5 ≦ I _SMAX /R≦9.4. The term “immediately after starting” means from when discharge is started between the electrodes to 4 seconds after that. This is because in the metal halide lamp for automobiles, as described above, high power and high current are input for 4 seconds from the start, and the discharge unit 11 is most loaded. This I _SMAX is about 0.5 seconds after the start in FIG. 2, but in the case where high power is temporarily turned on immediately before the start of 4 seconds in order to further increase the 4-second luminous flux, _SMAX appears in less than 4 seconds after starting. That is, I _SMAX / R can be changed not only by the diameter of the electrode to be used, but also by input power or power control. 2 can be obtained by an oscilloscope, and the value of I _SMAX can be obtained from the same figure.

  FIG. 3 is a view for explaining one specification of the metal halide lamp for an automobile headlamp shown in FIG. The following tests are performed based on this specification unless otherwise specified.

Discharge vessel 1: made of quartz glass, inner volume of discharge space 14 = 26.9 mm ³ , inner diameter A = 2.49 mm, outer diameter B = 6.19 mm, longitudinal sphere length C = 7.8 mm,
Metal halide 2: ScI ₃ = 0.136 mg, NaI = 0.218 mg, ZnI ₂ = 0.045 mg, InBr = 0.001 mg,
Noble gas: xenon = 13.5 atm,
Mercury: 0 mg,
Metal foils 3a1, 3b1: made of molybdenum,
Electrodes 3a2, 3b2: Triated tungsten, diameter R = 0.38mm, distance between electrodes D = 4.34mm (actual distance between electrodes = 3.74mm),
Coils 3a3, 3b3: made of doped tungsten
External lead wires 3a4, 3b4: made of molybdenum, diameter = 0.4 mm,
Maximum input power immediately after startup = 74 W, maximum current value immediately after startup I _SMAX = 2.9 A, I _SMAX /R=7.63 (A / mm), stable power = 34.5 W.

FIG. 4 is a diagram for explaining the illuminance maintenance ratio and 4-second light flux after 1000 hours of lighting when I _SMAX / R is changed, and FIG. 5 is a graph of FIG. The test condition is a flash cycle of the EU 120 minute mode defined in JEL215, which is a standard for an automobile headlamp HID light source. The illuminance maintenance rate indicates a temporal change of the light beam emitted from the upper part of the discharge unit 11 and is measured based on the “illuminance measurement method” of JIS C 7612.

As can be seen from the results, the illuminance maintenance ratio decreases as the value of I _SMAX / R increases. The cause of the decrease in the illuminance maintenance rate is related to the white turbidity generated on the inner wall of the upper part of the discharge part 11, and the cause of the white turbidity is considered to be heating of the inner wall surface of the upper part of the discharge part 11 by the arc 9. That is, when the value of I _SMAX / R is large, it is presumed that the energy of the arc 9 increases, the inner wall surface of the upper part of the discharge part 11 is strongly heated, and white turbidity is generated. According to FIG. 5, when I _SMAX / R is greater than 9.4 (A / mm), the decrease in the illuminance maintenance factor is increased, which is not desirable. On the other hand, the smaller the value of I _SMAX / R, the slower the temperature rise of the discharge part 11 and the lower the 4-second luminous flux. According to FIG. 5, when I _SMAX / R is smaller than 7.5 (A / mm), the decrease in the 4-second light flux is increased, which is not desirable. Therefore, it is necessary to set I _SMAX / R (A / mm) to 7.5 ≦ I _SMAX /R≦9.4. In order to suppress the white turbidity at the upper part of the discharge part 11, the curvature of the arc 9, etc. It is desirable to consider the effects of That is, the sealed pressure P (atm) of xenon, the distance D (mm) between the electrodes, the distance L (mm) from the upper end of the electrodes 3a2, 3b2 where the arc 9 is formed to the upper inner wall of the central portion in the axial direction of the discharge part 11 It is more effective to combine those suitably designed. However, in the use of automobile headlamps, the interelectrode distance D is an invariable value that can hardly be changed. Therefore, the xenon sealing pressure P and the distance L from the upper end of the electrode to the inner wall surface of the discharge unit 11 are as follows. You only have to think about it. Therefore, as a result of the test conducted by the inventor, it was found that if the distance L is increased, the cloudiness after 1000 hours of lighting can be suppressed even if the xenon sealing pressure P is increased. And when the number of test pieces was increased and the relationship between the sealed pressure P of xenon and the distance L was examined, if P ≦ 60.25L−48.90 was satisfied as shown in FIG. It was found that the illuminance maintenance rate was small and good. The distance L is limited to 1.20 mm from the viewpoint of design, and the xenon sealing pressure P is 13 atm or more, so the range that can be actually implemented is limited.

Therefore, in the present embodiment, when the maximum current value immediately after start is I _SMAX (A) and the diameter of the electrode is R (mm), I _SMAX / R (A / mm) is 7.5 ≦ I _SMAX By satisfying the relationship of /R≦9.4, the rise of the 4-second light beam can be accelerated while suppressing cloudiness and improving the life characteristics.

  Further, when the sealed pressure of xenon is P (atm) and the distance from the upper end of the electrode to the upper inner wall of the central portion in the axial direction of the discharge part is L (mm), P ≦ 60.25L−48.90 By satisfying the relationship, white turbidity can be further suppressed, and good life characteristics can be realized.

  The embodiment of the present invention is not limited to the above, and may be modified as follows, for example.

  The shape of the discharge space 14 may be substantially elliptical.

  The electrodes 3a2, 3b2 are not limited to triated tungsten electrodes, but may be electrodes made of pure tungsten, doped tungsten, rhenium tungsten, or the like.

The figure for demonstrating 1st Embodiment of the metal halide lamp for motor vehicle headlamps of this invention. The figure for demonstrating the time change of electric power and an electric current. The figure for demonstrating one specification of the metal halide lamp for motor vehicle headlamps of FIG. The figure for _{demonstrating} the illumination intensity maintenance factor after a 1000-hour lighting and 4-second light beam when I _SMAX / R is changed. FIG. 5 is a graph of FIG. The figure for demonstrating the relationship between the sealing pressure P of xenon and the distance L from the upper end of an electrode to the upper inner wall of the axial direction center part of a discharge part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Airtight container 11 Discharge part 12a, 12b Sealing part 13a, 13b Non-sealing part 14 Discharge space 2 Metal halide 3a, 3b Mount 3a1, 3b1 Metal foil 3a2, 3b2 Electrode 3a3, 3b3 Coil 3a4, 3b4 External lead wire 3c Support wire 4 Sleeve 5 Outer tube 6 Socket 71 Metal band 72 Tongue piece 8a Bottom terminal 8b Side terminal 9 Arc

Claims (2)

A discharge part in which a discharge space is formed; an airtight container having a pair of sealing parts formed at both ends of the discharge part; a discharge medium containing xenon and a metal halide enclosed in the discharge space; One end is sealed to the sealing portion, and the other end is provided with a pair of electrodes opposed to the discharge space, and the tube axis is disposed substantially horizontally, and is approximately twice as much as stable at the start-up. In metal halide lamps for automotive headlamps that are supplied with the above power,
The enclosed pressure of xenon in the discharge medium is 13 atm or more and essentially does not contain mercury,
The relationship of I _SMAX / R (A / mm) is 7.5 ≦ I _SMAX /R≦9.4, where I _SMAX (A) is the maximum current value immediately after starting and R (mm) is the diameter of the electrode. A metal halide lamp for automobile headlamps characterized by satisfying   When the sealed pressure of xenon is P (atm) and the distance from the upper end of the electrode to the upper inner wall of the central portion in the axial direction of the discharge part is L (mm), the relationship of P ≦ 60.25L−48.90 is established. The metal halide lamp for an automobile headlamp according to claim 1, wherein the metal halide lamp is satisfied.

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