JPH05290804A - Metal halide lamp for head lamp of automobile - Google Patents

Abstract

PURPOSE:To prevent electric discharge between an outside lead wire and an electric power supplying line inside an outer tube without covering the electric power supplying line with an insulator, and prevent starting deficiency and oxidation of the outside lead wire and the like by securely shielding the inside of the outer tube from outside air. CONSTITUTION:A light emitting tube 1 contained in an outer tube 2 is shielded from outside air by a sealing portion 3. Xenon is sealed inside the outer tube 2. An outside lead wire 4 introduced from the light emitting tube 1 and an electric power supplying line 6 connected to another outside lead wire 5 are connected to insulating covered electric wires 8a, 8b via molybdenum foils 7a, 7b of the sealing portion 3, respectively. The relationship expressed by 2Pd.L<Po.R is satisfied, wherein L (mm) represents a distance between electrodes of the light emitting tube 1; Pd (Pa), a pressure of xenon sealed inside the light emitting tube 1; R (mm), the shortest distance between the outside lead wire 4 and the electric power supplying line 6; and Po (Pa), a pressure of xenon sealed inside the outer tube 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal halide lamp for a vehicle headlight.

[0002]

2. Description of the Related Art In a conventional metal halide lamp for a vehicle headlight, xenon is enclosed in an arc tube in order to accelerate the rising of a luminous flux, and a high voltage pulse of ten and several kV is applied at the time of starting and restarting the lamp. I am trying. However, at this time, discharge occurs between one of the two external lead wires led out from the arc tube and the power supply line connected to the other external lead wire, which causes a disadvantage that the lamp does not light. Also, because there is water in the atmosphere,
The hydrogen in the water enters the arc tube and causes a start failure, and the oxygen in the water causes oxidation of the external lead wires and the like. Therefore, also in a metal halide lamp for a vehicle headlight, it is desirable to have a double tube structure in which a mount including an arc tube is shielded from the atmosphere like a general metal halide lamp.

Conventionally, as an example of a double tube structure, for example, in Japanese Utility Model Laid-Open No. 3-104949, one of two external lead wires led from an arc tube is connected to a power supply line, and this power supply is performed. By covering the wire with an insulator such as ceramics, it is possible to prevent discharge (hereinafter referred to as discharge in the outer tube) from occurring between the other outer lead wire and the power supply wire, and to open the outer end surface of the outer tube with the base. There is known a discharge lamp in which an arc tube is provided inside an outer tube by abutting on the discharge lamp.

[0004]

However, in such a discharge lamp, since the atmosphere between the outer tube and the base is not sufficiently shut off, water in the atmosphere may intrude into the outer tube from that interval. By the way, in order to prevent this, a structure in which the end portion of the outer tube is sealed may be used, but the structure of the discharge lamp described above has a problem that the sealing cannot be performed because of the insulator.

The present invention has been made in order to solve such a problem, does not cause discharge in the outer tube, can reliably shut off the inside of the outer tube from the atmosphere, and prevents a start failure and an oxidation of an external lead wire or the like. A metal halide lamp for a vehicle headlight having a double-tube structure that can be prevented.

[0006]

A metal halide lamp for a vehicle headlamp according to the present invention has a pair of electrodes therein, and an arc tube enclosing mercury, xenon and a metal halide is provided in the outer tube. Xenon is sealed in and the end of the outer tube is sealed, the xenon pressure in the arc tube is Pd (Pa), the distance between the electrodes of the arc tube is L (mm), and the xenon pressure in the outer tube is Po (P
a), where R (mm) is the shortest distance between the two conductors respectively connected to the pair of electrodes and led out from the arc tube, the relationship of 2Pd · L <Po · R is satisfied. .

[0007]

According to the present invention, the insulation voltage between the two conductors led out from the arc tube can be increased by the xenon enclosed in the outer tube, and by satisfying the above relational expression, the conductor can be insulated. Since it is not necessary to cover with, the end portion of the outer tube can be sealed, and the inside of the outer tube can be reliably shielded from the atmosphere.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view of a metal halide lamp for a 35 W automobile headlight according to an embodiment of the present invention.

In FIG. 1, mercury, ScI ₃ , NaI as a metal halide, and xenon as a starting gas are enclosed in a quartz arc tube 1 having a pair of electrodes therein. The arc tube 1 is an outer tube 2 made of quartz.
It is provided inside, and the end portion of the outer tube 2 is sealed to form the sealing portion 3 so as to be shielded from the outside air.
Xenon is enclosed inside the outer tube 2. The external lead wires 4 and 5 are led out from both ends of the arc tube 1, the external lead wire 4 is connected to the insulation-coated electric wire 8a via the molybdenum foil 7a of the sealing portion 3, and the external lead wire 5 is a power supply wire. Insulated electric wire 8 connected to 6 via molybdenum foil 7b
b respectively. The base 9 is made of a synthetic resin such as PPS (polyphenylene sulfide) and has an outer tube 2
It is fixed to the end of.

In the above structure, the xenon pressure inside the arc tube 1 is Pd (Pa), the interelectrode distance is L (mm), and the xenon pressure inside the outer tube 2 is Po (Pa), which is derived from the arc tube 1. The shortest distance between the external lead wire 4 and the power supply wire 6 connected to the external lead wire 5 was set to R (mm), and various lamps were manufactured by variously combining these. That is, there are six combinations of the xenon pressure Pd (Pa) in the arc tube 1 and the inter-electrode distance L (mm), as shown in Table 1.
Xenon pressure Po (Pa) in outer tube 2 and external lead wire 4-
As shown in Table 2, there are six combinations with the shortest distance R (mm) of the power supply line 6.

[0012]

[Table 1]

[0013]

[Table 2]

Further combining Tables 1 and 2, 36
Using the lamp manufactured as described above, the presence or absence of discharge in the outer tube at the time of starting and restarting was examined. As the test pulse, a pulse having a peak value of 15 kV was applied. The measurement at the time of starting was performed with the lamp turned on for 10 minutes or more and then left for 1 hour or more after the light was turned off, and the measurement at the time of restart was performed after turning on the lamp for 10 minutes or more and 30 seconds after the light was turned off.

Regarding the relationship between Pd · L and Po · R, the xenon pressure Pd (Pa) in the arc tube 1 and the inter-electrode distance L (m
m) and xenon pressure inside outer tube 2 Po (Pa)
Distance between the external lead wire 4 and the power supply wire 6 and R (m
The result of rearranging the product with m) as a parameter is shown in FIG. In FIG. 2, a circle mark indicates that the discharge inside the outer tube did not occur at the time of starting and restarting, and a mark Δ indicates that the discharge inside the outer tube did not occur at the time of starting, but the discharge inside the outer tube occurred at the time of restarting. Indicates that the discharge in the outer tube occurred at the time of starting and restarting. As is clear from FIG. 2, when the condition of 2Pd.L <Po.R is satisfied, it is understood that the discharge in the outer tube does not occur at the time of starting and restarting. That is, if this condition is satisfied, it is possible to realize a double-tube structure in which electric discharge in the outer tube does not occur at the time of starting and restarting without covering the power supply line 6 with an insulator, and the power supply line 6 is made of an insulator. Since it is not necessary to cover
The end of the outer tube 1 can be sealed, and the inside of the outer tube 2 can be reliably shielded from the atmosphere. As a result, the arc tube 1 is always provided in the xenon atmosphere which is the inert gas in the outer tube 2, so that the external lead wires 4, 5
Since there is no risk of oxidation such as the above, and there is no risk of hydrogen existing in the atmosphere penetrating into the arc tube 1, good starting characteristics can be obtained.

[0016]

As described above, according to the present invention, the xenon pressure in the arc tube is Pd (Pa) and the distance between the electrodes is L (m).
m), the xenon pressure inside the outer tube is Po (Pa), and the shortest distance between the two conductors derived from the arc tube is R (mm), by satisfying the relationship of 2Pd · L <Po · R, Since it is not necessary to cover the conductor inside the outer tube with an insulator, the outer tube can be sealed, and the inside of the outer tube can be reliably shielded from the atmosphere. Therefore, the arc tube can always be placed in the xenon atmosphere, which is an inert gas in the outer tube, and it is possible to prevent oxidation of the external lead wires, etc. Furthermore, hydrogen existing in the atmosphere enters the arc tube. Therefore, a metal halide lamp for a vehicle headlamp having a good starting characteristic can be provided.

[Brief description of drawings]

FIG. 1 is a front view of a metal halide lamp for a vehicle headlight according to an embodiment of the present invention.

FIG. 2 shows the product Pd · L of the xenon pressure Pd in the arc tube and the distance L between the electrodes, the xenon pressure Po in the outer tube and the external lead wire.
The figure which shows the relationship with the product Po * R of the shortest distance R between power supply lines.

[Explanation of symbols]

 1 Arc Tube 2 Outer Tube 3 Sealing Part 4, 5 External Lead Wire 6 Power Supply Wire 7a, 7b Molybdenum Foil 8a, 8b Insulation Coated Electric Wire 9 Base

Claims (1)

[Claims] 1. An arc tube having a pair of electrodes inside and containing mercury, xenon and a metal halide is provided in the outer tube, xenon is sealed in the outer tube, and an end portion of the outer tube is sealed. The pressure of xenon in the arc tube is Pd (Pa), and the distance between the electrodes of the arc tube is L (m).
m), when the xenon pressure in the outer tube is Po (Pa) and the shortest distance between the two conductors respectively connected to the pair of electrodes and led out from the arc tube is R (mm), 2
A metal halide lamp for a vehicle headlight, characterized by satisfying a relationship of Pd · L <Po · R.