JP2001110358A - Discharge bulb - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the possibility that the emission tube portion of an arc tube composed so that an arc tube is almost concentrically surrounded by a shroud tube will be fructured during lighting of the arc tube. SOLUTION: Clearance g1 between the uppermost point P1 on outer face 20e of emission tube portion 20a and inner wall face 18c of shroud tube 18 is set at g1 >=0.3 mm based on the prescribed experimental result. This prevents rapid creation of devitrification by heat accumulation phenomenon and dopant diffusion phenomenon to develop many micro-cracks at the upper end where temperature becomes the highest in the emission tube portion 20a during the lighting of the discharge valve. As a result, generation of an explosion of the emission tube portion 20a with the micro-cracks as the starting points can be prevented in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge bulb used for a vehicle headlamp and the like, and more particularly to a discharge bulb configured so that an arc tube is substantially concentrically surrounded by a shroud tube.

[0002]

2. Description of the Related Art In recent years, discharge bulbs have been widely used for vehicle headlamps and the like since they can emit high-luminance light.

[0003] As a discharge bulb used for a vehicle headlamp or the like, a discharge bulb including an arc tube 102, a shroud tube 104, and an insulating plug 106 as shown in FIG. 5 is known. In the arc tube 102, a substantially elliptical arc tube part 102a is formed in the middle part of the elongated glass tube extending in the horizontal direction in the axis Ax direction, and a pair of pinch seal parts 102b are formed on both sides in the axis Ax direction. Also, the shroud tube 104 surrounds the arc tube 102 substantially concentrically so that the axis A
It extends in the x direction and is welded to the arc tube 102 at both ends in the axis Ax direction. The insulating plug 106 fixedly supports the arc tube 102 and the shroud tube 104.

[0004]

In this discharge bulb, since the shroud tube 104 is welded to the arc tube 102 at both ends in the direction of the axis Ax, there is a certain degree of positional relationship between the two due to the characteristics of the welding method. Inevitably occurs. The discharge bulb is connected to the arc tube section 10 of the arc tube 102.
2a and the shroud tube 104 are close to each other.
a may come into contact with the shroud tube 104.

However, the arc tube section 102
When a discharge bulb in which a is in contact with the shroud tube 104 is used, there is a problem that the arc tube portion 102a bursts during lighting.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and in a discharge bulb having a structure in which an arc tube is substantially concentrically surrounded by a shroud tube, an arc tube portion of the arc tube during lighting is provided. It is an object of the present invention to provide a discharge bulb that can eliminate the possibility of explosion.

[0007]

SUMMARY OF THE INVENTION The present invention achieves the above object by devising the clearance between a predetermined portion of the arc tube portion and a shroud tube based on the result of elucidating the cause of the rupture of the arc tube portion. It is like that.

That is, the discharge bulb according to the present invention comprises:
An arc tube in which a substantially elliptical spherical arc tube portion is bulged at an axially intermediate portion of an elongated glass tube extending in a horizontal direction, and a pair of pinch seal portions are formed on both sides of the arc tube portion in the axial direction. And a shroud tube extending in the axial direction so as to substantially concentrically surround the arc tube and welded to the arc tube at both ends in the axial direction, and an insulating plug for fixedly supporting the arc tube and the shroud tube. In the discharge bulb provided, a clearance g1 between an uppermost point on an outer peripheral surface of the arc tube portion and an inner peripheral surface of the shroud tube is set to g1 ≧ 0.3 mm. .

The above-mentioned "the highest point on the outer peripheral surface of the arc tube part"
The size of the clearance between the other points and the inner peripheral surface of the shroud tube is not particularly limited as long as they are not in contact with each other.

[0010]

As described above, in the discharge bulb according to the present invention, the uppermost point on the outer peripheral surface of the arc tube portion of the arc tube and the inner peripheral surface of the shroud tube surrounding the arc tube substantially concentrically. Clearance with g1
Is set to satisfy g1 ≧ 0.3 mm, the following operation and effect can be obtained.

In other words, if the arc tube portion of the arc tube is in contact with the shroud tube, when the discharge bulb is turned on, a heat stagnation phenomenon occurs in a portion of the arc tube portion near the contact portion. Also, generally, the shroud tube contains a dopant for the purpose of cutting off ultraviolet rays,
This causes a phenomenon in which the dopant diffuses into the arc tube portion through the contact portion. Then, due to such a thermal cage phenomenon and a dopant diffusion phenomenon, abrupt devitrification occurs in a portion near the contact portion in the arc tube portion, whereby a large number of microcracks are generated in the portion, and the starting point is defined as a starting point. The rupture of the light emitting tube part occurs.

By the way, the temperature of the arc tube portion of the arc tube at the time of lighting the discharge bulb differs depending on the portion, and the highest temperature is about 1000 ° C. at the upper end portion. Therefore, when the arc tube comes into contact with the shroud tube at the upper end portion, the heat trapping phenomenon and the dopant diffusion phenomenon become most remarkable, and the arc tube tends to be ruptured.

For this reason, it is effective to prevent the upper end of the arc tube portion from contacting the shroud tube in order to prevent the arc tube portion from bursting. However, at that time, it is not enough to simply make it non-contact, and it is evident from the results of experiments conducted by the inventors that the arc tube part may burst if it is in a very close state. It was revealed. The reason for this is that even if the upper end of the arc tube is not in contact with the shroud tube when the discharge bulb is not lit, a certain period of time after the discharge bulb is lit causes thermal expansion of the arc tube and the shroud tube. It is thought to be due to contact.

From the results of this experiment, it was found that the clearance g1 between the uppermost point on the outer peripheral surface of the arc tube portion and the inner peripheral surface of the shroud tube was g1 ≧ 0.3 mm as in the present invention.
It has become clear that if the setting is made, it is possible to prevent the rupture of the arc tube portion from occurring.

As described above, according to the present invention, in a discharge bulb configured so that an arc tube is substantially concentrically surrounded by a shroud tube, it is possible to eliminate the possibility that the arc tube portion of the arc tube bursts during lighting. Can be.

The above "the highest point on the outer peripheral surface of the arc tube portion"
As described above, the size of the clearance between the other points and the inner peripheral surface of the shroud tube is not particularly limited. In many cases, it is difficult to secure 0.3 mm or more. Therefore, in such a case, the clearance g1 between the uppermost point on the outer peripheral surface of the arc tube portion and the inner peripheral surface of the shroud tube is determined by the clearance g1 between the lowermost point on the outer peripheral surface of the arc tube portion and the inner peripheral surface of the shroud tube. g1> g2 for g2,
It is preferable to preferentially secure the clearance at the upper end where the temperature is highest in the arc tube portion.

In the above configuration, the clearance g1 between the uppermost point on the outer peripheral surface of the arc tube portion and the inner peripheral surface of the shroud tube is not particularly limited as long as g1 ≧ 0.3 mm. G1 ≦ 3.0 mm
Is preferably set for the following reason.

That is, when the discharge bulb is turned on, the arc tube section is maintained in a state of being kept warm by the shroud tube surrounding the arc tube section. It decreases rapidly. Therefore, the clearance g1 is changed to g1
It is preferable to set ≦ 3.0 mm.

In the above configuration, the arc tube and the shroud tube may be fixedly supported on the insulating plug at an angular position such that both pinch seal portions extend substantially horizontally in the axis direction of the arc tube. The following operation and effect can be obtained.

That is, the pinch seal portion is formed by pressing the elongated glass tube into which the electrode assembly is inserted from both sides. At this time, the elongated glass tube is deformed into a flat shape. The part also slightly deforms from an elliptical sphere to a flat elliptical sphere. Therefore, if the arc tube is fixedly supported on the insulating plug at an angular position where the two pinch seal portions extend substantially horizontally in the horizontal direction with respect to the axis of the arc tube, a portion having a small outer diameter in the arc tube portion is obtained. Can be located at the upper end. Thus, even when the inner diameter of the shroud tube is small, the clearance g1 between the uppermost point on the outer peripheral surface of the arc tube portion and the inner peripheral surface of the shroud tube is set to g1 ≧
It is relatively easy to set it to 0.3 mm.

In addition, since both pinch seal portions are pressed so as to extend substantially flat in the horizontal direction, the vertical displacement of the electrodes of both electrode assemblies can be reduced, thereby improving the light distribution characteristics of the lamp. Can be done.

Here, the "substantially horizontal direction" means a direction within ± 5 ° with respect to a horizontal plane.

[0023]

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

FIG. 1 is a side sectional view showing a discharge bulb 10 according to an embodiment of the present invention.

As shown in the figure, a discharge bulb 10 according to the present embodiment has an arc tube unit 1 extending in the front-rear direction.
2 and an insulating plug 14 for fixing and supporting the rear end of the arc tube unit 12.

The arc tube unit 12 includes an arc tube 16 positioned on an axis Ax extending in the front-rear direction,
A shroud tube 18 that surrounds the arc tube 16 substantially concentrically is formed integrally.

The arc tube 16 comprises an arc tube body 20 formed by processing an elongated cylindrical quartz glass tube, and a pair of front and rear electrode assemblies 22A and 22B embedded in the arc tube body 20. .

The arc tube main body 20 has a substantially elliptical spherical arc tube portion 20a bulging at a predetermined position in the direction of the axis Ax, and pinch seal portions 20b1 on both front and rear sides thereof.
20b2 are formed.
The front and rear sides of b1 and 20b2 are cylindrical portions 20c1 and 20c2.
Although it is left as it is, an annular flange portion 20d is formed on the rear cylindrical portion 20c2. In the arc tube portion 20a of the arc tube body 20, a discharge space 24 in which xenon gas and a luminescent substance are sealed is formed.

The shroud tube 18 is a cylindrical quartz glass tube containing a dopant for the purpose of cutting off ultraviolet rays or the like, and has a cylindrical portion 20c1 of the arc tube body 20 and a flange portion 2 at its front and rear ends 18a and 18b.
0d.

Each of the electrode assemblies 22A and 22B is formed by connecting and fixing electrode rods 26A and 26B and lead wires 28A and 28B via molybdenum foils 30A and 30B, and the arc tube body 20 at each of the pinch seal portions 20b1 and 20b2. Is pinch sealed. At that time, the molybdenum foils 30A and 30B are all pinch-sealed portions 20b.
1, 20b2, each electrode rod 26A,
The lead wire 26B projects into the discharge space 24 such that the tip ends face each other from both front and rear sides, and the lead wires 28A and 28B are respectively connected to the cylindrical portions 20c1 and 20c2.
It extends to the front and rear of the arc tube main body 20 through the inside. Each of these lead wires 28A and 28B is made of a molybdenum wire.

A metal band 36 is fixed to the outer peripheral surface of the rear end of the shroud tube 18.
, A slider fitting 38 is connected and fixed by laser welding. The slider fitting 38 is
With the metal band 36 engaged with the arc tube unit 1 with the rear end face of the slider fitting 38 as the reference plane.
2 after the first alignment of metal band 36
The connection is fixed.

The insulating plug 14 has a base plate 42 fixed to the front end of the insulating plug body 40.
A slider fitting 38 on the arc tube unit 12 side is connected and fixed to the base plate 42 by laser welding. At this time, the base plate 42 comes into contact with the slider fitting 38 by surface contact, so that the arc tube unit 12 can be connected and fixed after the secondary alignment.

FIG. 2 is an enlarged view of a portion II in FIG.
FIG. 3 is an enlarged cross-sectional view taken along the line III-III of FIG. 2.

In these figures, the uppermost point P on the outer peripheral surface 20e of the arc tube portion 20a of the arc tube body 20 is shown.
1 and the clearance g1 between the inner peripheral surface 18c of the shroud tube 18 are set to g1 ≧ 0.3 mm.
The reason for setting such a value is as follows.

That is, if the arc tube portion 20a of the arc tube body 20 is in contact with the shroud tube 18, when the discharge bulb 10 is turned on, a heat stagnation phenomenon occurs in a portion of the arc tube portion 20a near the contact portion, Further, a phenomenon occurs in which the dopant contained in the shroud tube 18 diffuses into the arc tube portion 20a through the contact portion. Then, due to such a heat sinking phenomenon and a dopant diffusion phenomenon, abrupt devitrification occurs in a portion near the contact portion in the arc tube portion 20a, whereby a large number of microcracks are generated in the portion, and the starting point is generated. The rupture of the arc tube portion 20a occurs.

Incidentally, the temperature of the arc tube portion 20a when the discharge bulb is lit differs depending on the portion. For example, the lower end of the arc tube portion 20a is about 700 ° C., while the upper end is about 1000 ° C., which is the highest. Therefore, when the arc tube portion 20a comes into contact with the shroud tube at the upper end portion, the phenomenon of thermal stagnation and the diffusion of the dopant become most remarkable, and the arc tube portion 20a is easily ruptured.

Therefore, it is effective to prevent the upper end of the arc tube portion 20a from contacting the shroud tube 18 in order to prevent the arc tube portion 20a from bursting. However, at this time, it is not sufficient to simply make the light-emitting device non-contact.
It has been clarified from the results of the following experiments conducted by the inventors that bursting of a may occur.

Table 1 and FIG. 4 show the arc tube section 20 when the discharge bulbs having different clearances g1 are lit.
5 shows the results of an experiment in which the burst occurrence rate and light flux of a were measured.

[0039]

[Table 1]

As shown in Table 1, the burst occurrence rate was measured for ten samples for each of 11 types of clearance g1 having different sizes. As these samples, those whose arc tube body 20 was made of quartz glass and whose arc tube portion 20a had a thickness of 1.5 mm were used. For the light flux, clearance g1 = 0
(Ie, the sample in which the upper end portion of the arc tube portion 20a is in contact with the shroud tube 18) as a reference (100%), and the measurement results of the luminous flux of the sample having a clearance g1 of other size are obtained. Expressed as a relative percentage.

As is clear from Table 1 and FIG. 4, when the clearance g1 is g1 ≧ 0.3 mm, the arc tube portion 20a
When g1 <0.3 mm, the upper end of the arc tube portion 20a and the shroud tube 18 do not rupture.
As a result, rupture of the arc tube portion 20a occurs not only when the arc tube is in contact but also when the arc tube is not in contact.

The reason for this is that even when the upper end of the arc tube portion 20a is not in contact with the shroud tube 18 when the discharge bulb 10 is not turned on, the arc tube is turned on after a certain period of time while the discharge bulb 10 is turned on. It is considered that the thermal expansion of the portion 20a (largest at the upper end portion) causes the shroud tube 18 to come into contact.

From the experimental results, in the discharge bulb 10 according to the present embodiment, the clearance g1 between the uppermost point P1 on the outer peripheral surface 20e of the arc tube portion 20a of the arc tube main body 20 and the inner peripheral surface 18c of the shroud tube 18 is shown.
Is set to g1 ≧ 0.3 mm, so that the arc tube part 2
The burst of 0a is prevented from occurring.

In FIGS. 2 and 3, the clearance g1 is set between the lowermost point P2 on the outer peripheral surface 20e of the arc tube portion 20a of the arc tube main body 20 and the shroud tube 1.
G1 with respect to the clearance g2 between the inner peripheral surface 18c and the inner peripheral surface 18c>
g2. The reason is as follows.

That is, if it is assumed that the clearance between the outer peripheral surface 20e of the arc tube portion 20a and the inner peripheral surface 18c of the shroud tube 18 is constant over the entire circumference when the discharge bulb 10 is not lit, Due to the thermal expansion of the arc tube portion 20a, the shroud tube 18
The portion that is likely to contact the upper end portion where the temperature is highest in the arc tube portion 20a, and other portions are less likely to contact the shroud tube 18 than the upper end portion. Therefore,
By setting g1> g2, the inner diameter of the shroud tube 18 can be set to a small value while preventing the arc tube portion 20a from bursting.

As is clear from Table 1 and FIG. 4, in the region where the clearance g1 is g1 ≧ 0.3 mm, the luminous flux tends to gradually decrease as the clearance g1 increases, and g1 = 3.0. The luminous flux tends to rapidly decrease from around.

When the discharge bulb 10 is turned on, the arc tube section 20a is kept warm by the shroud tube 18 surrounding it.
Is considered to be too far from the arc tube portion 20a, because the heat retaining effect is rapidly weakened.

Therefore, from the above experimental results, it is preferable that the clearance g1 is set so that g1 ≦ 3.0 mm.

In this embodiment, FIGS. 2 and 3
As shown in FIG. 5, the arc tube unit 12 is fixedly supported on the insulating plug 14 at an angular position such that the pinch seal portions 20b1 and 20b2 extend flat in the horizontal direction with respect to the axis Ax. The reason why the fixed support is performed at such an angular position is as follows.

That is, each pinch seal portion 20b1, 2
Ob2 is formed by pressing the elongated glass tube into which the electrode assemblies 22A and 22B are inserted from both sides. At this time, since the elongated glass tube is deformed into a flat shape,
Accordingly, the arc tube portion 20a is slightly deformed from an elliptical sphere to a flat elliptical sphere. Therefore, if the arc tube unit 12 is fixedly supported on the insulating plug 14 at an angular position where the pinch seal portions 20b1 and 20b2 extend flat in the horizontal direction with respect to the axis Ax, the arc tube portion 2
At 0a, a portion having a small outer diameter can be arranged at the upper end. Thus, even when the inner diameter of the shroud tube 18 is small, the clearance g
It is relatively easy to set 1 to g1 ≧ 0.3 mm.

As described in detail above, the discharge bulb 10 according to the present embodiment includes the arc tube section 2 of the arc tube body 20.
0a, the clearance g1 between the uppermost point P1 on the outer peripheral surface 20e and the inner peripheral surface 18c of the shroud tube 18 is g1.
Since it is set to ≧ 0.3 mm, it is possible to eliminate the possibility that the arc tube portion 20a will burst during lighting.

When the thickness of the arc tube portion 20a is set to a value smaller than usual, the clearance g1 is set.
Is desirably set to a relatively large value from the viewpoint of effectively preventing the arc tube portion 20a from bursting.

In this embodiment, the clearance g1 is set to satisfy g1> g2 with respect to the clearance g2 between the lowest point P2 on the outer peripheral surface 20e of the arc tube portion 20a and the inner peripheral surface 18c of the shroud tube 18. Therefore, it is possible to set the inner diameter of the shroud tube 18 to a small value while preventing the arc tube portion 20a from bursting.

Further, in the present embodiment, since the clearance g1 is set to satisfy g1 ≦ 3.0 mm,
A sufficient heat retaining effect of the arc tube portion 20a by the shroud tube 18 can be ensured, so that the luminous flux can be maintained at a high value.

In this embodiment, the arc tube unit 12 is fixedly supported on the insulating plug 14 at an angular position such that the pinch seal portions 20b1 and 20b2 extend flat in the horizontal direction with respect to the axis Ax. In the arc tube portion 20a, a portion having a small outer diameter can be arranged at the upper end portion, so that the clearance g1 is set to g1 ≧ 0.3 mm even when the inner diameter of the shroud tube 18 is small. Is relatively easy. In addition, both pinch seal portions 20b1, 2
0b2 is pressed so as to extend flat in the horizontal direction, so that the electrode rods 26A, 26B of the two electrode assemblies 22A, 22B are pressed.
6B can be reduced in the vertical direction, whereby the light distribution characteristics of the lamp can be improved.

In this case, as shown in FIG.
Regarding x, even if the pinch seal portions 20b1 and 20b2 do not extend exactly flat in the horizontal direction, if the angle range is within ± 5 ° with respect to the horizontal plane, the same operation and effect as in the present embodiment can be obtained. it can.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a discharge bulb according to an embodiment of the present invention.

FIG. 2 is an enlarged view of part II in FIG.

FIG. 3 is an enlarged cross-sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a diagram showing a result of an experiment related to the embodiment.

FIG. 5 is a view similar to FIG. 1, showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Discharge bulb 12 Arc tube unit 14 Insulation plug unit 16 Arc tube 18 Shroud tube 18a Front end 18b Rear end 18c Inner peripheral surface 20 Arc tube main body 20a Light emitting tube part 20b1, 20b2 Pinch seal part 20c1, 20c2 Cylindrical part 20d Flange part 20e Outer peripheral surface 22A, 22B Electrode assembly 24 Discharge space 26A, 26B Electrode rod 28A, 28B Lead wire 30A, 30B Molybdenum foil 36 Metal band 38 Slider fitting 40 Insulating plug 42 Base plate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshitaka Oshima 500 Kitawaki, Shimizu City, Shizuoka Prefecture Inside Koito Manufacturing Shizuoka Plant (72) Inventor Yuichi Nagasawa 500 Kitawaki Shimizu City, Shizuoka Prefecture Koito Manufacturing Shizuoka Plant F term (reference) 5C043 AA14 BB09 CC01 CD01 CD05 DD01 EA19 EC20

Claims (4)

[Claims] An elongated glass tube extending in a horizontal direction has a substantially elliptical spherical arc tube portion bulging at an intermediate portion in the axial direction, and a pair of pinch seal portions are formed on both sides of the arc tube portion in the axial direction. An arc tube that extends in the axial direction so as to substantially concentrically surround the arc tube, and a shroud tube welded to the arc tube at both ends in the axial direction, and fixedly supports the arc tube and the shroud tube. And a clearance g1 between an uppermost point on an outer peripheral surface of the arc tube portion and an inner peripheral surface of the shroud tube is set to g1 ≧ 0.3 mm. And discharge bulb. 2. The clearance g1 is set to satisfy g1> g2 with respect to a clearance g2 between a lowermost point on an outer peripheral surface of the arc tube portion and an inner peripheral surface of the shroud tube. The discharge bulb according to claim 1, wherein 3. The apparatus according to claim 1, wherein the clearance g1 is set so that g1 ≦ 3.0 mm.
The discharge bulb as described. 4. The fixed support of the arc tube and the shroud tube to the insulating plug is performed at an angular position such that the pinch seal portions extend substantially horizontally in the horizontal direction with respect to the axis. The discharge bulb according to any one of claims 1 to 3, wherein