GB2352870A

GB2352870A - Discharge bulb with bent lead

Info

Publication number: GB2352870A
Application number: GB0014221A
Authority: GB
Inventors: Yoshitaka Ohshima; Shinichi Irisawa; Yasuyoshi Numajiri
Original assignee: Koito Manufacturing Co Ltd
Current assignee: Koito Manufacturing Co Ltd
Priority date: 1999-06-15
Filing date: 2000-06-09
Publication date: 2001-02-07
Anticipated expiration: 2020-06-09
Also published as: JP3657461B2; GB2352870B; DE10029107A1; GB0014221D0; NL1015426C2; JP2000357492A; NL1015426A1

Abstract

Discharge bulb 10 comprising an arc tube unit 12, pinch seal portions 20b1, 20b2 and lead 28B which is bent. The lead 28B may be bent in a zigzag, spiral or helical configuration and may be point symmetric. The bend or flexion may be formed by crimping between metal moulds. The bulb may comprise an insulating plug 14 for securing the arc tube unit 12 with a lead passage hole 40g and a terminal cap 42 for securing the end of the lead. The lead may be composed of molybdenum wire which is annealed and possesses an expansion property of 5-25%. A method of assembling an arc tube to an insulating plug where a lead including a bend or flexion extends from a rear pinch seal of the tube comprising: inserting the lead through a terminal cap on the plug unit, applying a tensile load to an end portion of the lead thereby expanding the flexion and securing the end portion of the lead to the terminal cap. Any portion of the lead that extends from the terminal cap may be removed and the lead may be secured to the terminal cap by laser welding.

Description

2352870 DISCHARGE BULB The present invention relates to discharge bulbs

used for illumination. More specifically, the present invention relates to discharge bulbs for automotive vehicle headlamps and the illumination applications.

In recent years, discharge bulbs have been often used for automotive vehicle headlamps and similar applications because of their capability for high intensity illumination.

Referring to FIG. 7, discharge bulbs having an arc tube 102 extending in the fore-and-aft direction and an insulating plug 104 for securing the rear end of the arc tube 102 are used for automotive vehicle headlamps. In these discharge bulbs, a lead 108 extends from the pinch seal section 106a situated at the rear of the arc tube body 106 of the arc tube 102 towards the insulating plug 104. This type of discharge bulb provides, at the front end of insulating plug 104, a securing portion 104a for securing the arc tube body 106 (via a shroud tube 110). The' rear end of the insulating plug 104 provides a lead passage hole 104b for passing a lead therethrough. The rear end of the insulating plug 104 of the discharge bulb, provides a terminal fitting 112 for securing the distal end. portion of the lead 108.

In the discharge bulb having such a structure as described above, the lead 108 of which both ends 1.0 are fixed, is subject to large thermal deformations because the temperature of the lead 108 varies substantially according to the on and off operation of the discharge bulb.

However, in the conventional discharge bulb described above, the lead 108 has virtually no margin for thermal expansion and contraction since it linearly extends in a simple manner as shown in FIG. 7. Therefore, the lead 108 undergoes significant thermal stress. In some instances, the lead 108 may be damaged, which can result in total failure of the discharge bulb.

Accordingly, it is an object of the present - 2 - invention to provide a discharge bulb that protects the lead from thermal stress damage that can result in a total failure of the discharge bulb.

The present invention is intended to achieve the object described above by improving the structure of the lead.

In other words, a discharge bulb according to the present invention comprises:

an arc tube including an arc tube body extending in the fore-and-aft direction and a lead extending from a pinch seal portion situated at the rear of the arc tube body toward the rear; an insulating plug provided at the front end thereof with a securing portion for securing the arc tube body and at the rear end thereof with a lead passage hole for passing the lead through; and a terminal fitting mounted at the rear end of the insulating plug for securing the distal end portion of the lead; wherein there is provided a flection in the intermediate region of the lead between the rear pinch seal portion and the distal end portion.

The 'flection" described above is not limited to a specific configuration. Configurations having a margin for deformation that provide for thermal expansion and contraction of the lead between the rear pinch seal portion and the distal end portion.

A z i g z a g, helical or a spiral shape my be employed.

As shown above, the discharge bulb according to the present invention is provided with a flection between the rear pinch seal portion and the distal end portion of the lead which extends from the rear pinch seal portion of the arc tube body toward the rear of the discharge bulb. Therefore, even when thermal deformation due to on and off operation of the discharge bulb occurs, the resultant expansion or contraction of the lead can be absorbed by the deformations of the flection, and thus a substantial thermal stress can be prevented from being exerted on the lead.

Therefore, according to the present invention, the lead of the discharge bulb is protected from damage resulting from a thermal stress that may cause the discharge bulb to fail.

While the configuration of the flection is not specifically limited as described above, a flection - 4 - having a point-symmetrical configuration has the following advantages.

While applying a bending process to the lead forms the flection, the configuration of a flection is subject to deformation from the initial configuration by spring back action after completion of the bending process. Such a deformation may cause a difference in the direction of axis of the lead between the proximal end portion and the distal end portion, and thus it may be difficult to pass the distal end portion of the lead into a lead passage hole formed on the insulating plug. By forming the flection with a point- symmetr i cal shape, even if the configuration of the flection were changed from the initial configuration by the spring back action, the deformation would also be almost point-symmetrical, and consequently, any differences in the direction of axis of the lead between the proximal end portion and the distal end portion can be effectively prevented. Therefore, the distal end portion can be passed easily through the lead passage hole formed on the insulating plug.

Since the direction of the axis of the lead at - 5 - the proximal end portion and the distal end portion are almost identical. During the process of pinch-sealing the electrode assembly (including the lead to the pinch seal portion at the rear of the arc tube), the electrode assembly may be inserted into the quartz glass tube, which is to be an arc tube body, with ease.

While the material that forms the "lead" is not limited to a specific material, in general, molybdenum is used. When the lead is formed of molybdenum as described above, it is preferable to use molybdenum wire annealed to possess an expansion property of 5% to 25%.. In other words, with an expansion property less than 5%, the lead cannot suppress the spring back action resulting from bending process. On the contrary, with an expansion property more than 25%, the lead can become embrittled due to recrystallization that occurred during annealing with an expansion property of -greater than 25%, the lead may be easily broken during bending process. Therefore, it is preferable to determine the expansion property within the range described above to avoid such disadvantages. As used herein, the term 'expansion property" means a longitudinal deformation that may occur on the molybdenum wire before it is broken when a tensile load-is applied to the molybdenum wire.

A particular embodiment in accordance with this invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side elevation illustrating a discharge bulb according to an embodiment of the present invention; FIG. 2 is an enlarged view of the part II of FIG.

10. 1; FIG. 3 (a) illustrates the process of assembling an arc tube unit constituting the discharge bulb to an insulating plug unit, wherein the lead is inserted into the insulating plug unit; FIG. 3 (b) illustrates the process of assembling an arc tube unit constituting the discharge bulb to an insulating plug unit, wherein the arc tube unit and the insulating plug unit are laser welded together; FIG. 3 (c) illustrates the process of assembling an arc tube unit constituting the discharge bulb to an insulating plug unit, wherein the lead is laser welded to a terminal cap; - 7 FIG. 4 (a) illustrates a process to form a flection of the lead, wherein the lead is placed between two metal molds; FIG. 4(b) illustrates a process to form a flection of the lead, wherein the lead is crimped by the two metal molds and undergoes a bending process; FIG. 4(c) illustrates the resultant configuration for the flection of the lead as formed by the two metal molds; FIG. 5(a) illustrates a flection of the lead that is formed in a point- s ymmetri cal manner; FIG. 5(b) illustrates a flection of the lead that is formed in a point- symmetrical manner with a centerline; FIG. 5(c) illustrates a deformation of a lead with a flection that was not formed in a pointsymmetrical manner; FIG. 5(d) illustrates an uncompensated deformation of a lead with a flection that was not formed in a point-symmetrical manner, wherein the lead does not spring back to its original configuration; FIG. 6(a) illustrates a modification of the - 8 assembly process, wherein the flection contacts the rear cylindrical portion of the shroud tube as the lead is inserted into the insulating plug; FIG. 6(b) illustrates tension being applied to the lead after it is inserted through the terminal cap, thereby preventing the f lection of the lead from contacting the rear cylindrical portion of the shroud tube; and FIG. 7 illustrates a conventional discharge bulb.

FIG. I is a sectional side elevation of the discharge bulb 10 according to one embodiment of the invention and FIG. 2 is an enlarged view of the part II of FIG. 1.

As shown in FIGS. 1 and 2, the discharge bulb 10 according to the present invention comprises an arc tube unit 12 extending in the fore-and-aft direction and an insulating plug unit 14 for securing the rear end of the arc tube unit 12.

The arc tube unit 12 comprises an arc tube 16 9 and a shroud tube 18 surrounding the arc tube 16.

The arc tube 16 and the shroud tube 18 form a unitary assembly.

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

The arc tube body 20 has a light emitting tube portion 20a of nearly ellipsoidal shape in the center, and pinch. seal portions 20bl, 20b2 at the front and rear of the light emitting tube portion 20a. Both front and rear sides of these pinch seal.portions 20bl-, 20b2 remain as cylindrical portions 20cl, 20c2. In the light emitting tube portion 20a of the arc tube body 20, there is formed a discharging space 24 filled with xenon gas and other chemicals.

The shroud tube 18 is a cylindrical quartz glass tube of which the front and back ends are welded to the cylindrical portions 20cl, 20c2.

The respective electrode assemblies 22A, 22B are composed of electrode rods 26A, 26B and leads 28A, 28B secured with each other via molybdenum foils 30A, 30B, and are pinch-sealed at the respective pinch seal portions 20bl, 20b2 to the arc tube body 20.

While the molybdenum foils 30A, 30B are completely embedded within-the pinch seal portions 20bl, 20b2, the electrode rods 26A, 26B project from the rear and front sides of the pinch seal portions 20bl, 20b2 into the discharging space 24 with their tips opposed with each other. The leads 28A, 28B extend through the cylindrical portions 20cl, 20c2 out from the front and rear of the arc tube body 20. These leads 28A, 28B are both formed of molybdenum wires. The lead 28B used on the rear side is heat-treated (annealed) so as to possess an expansion property of 5% to 25%.

The lead 28A situated on the front side of the discharge bulb 10 is formed linearly and the portion in the vicinity of the front end thereof is spot welded to a L-shaped lead 32. The L-shaped lead 32 is surrounded by a sleeve 34 and extends rearwardly in parallel with the arc tube unit 12.

On the other hand, the lead 28B situated on the rear side of the discharge bulb 10 is formed in such a manner that the proximal end portion (front end portion) 28Ba and the distal end portion (rear end portion) 28Bb are o f linear shapes and the intermediate section which is to be received in the cylindrical portion 20c2 of the arc tube body 20 is formed as a flection 28Bc in a zigzag shape. The f lection 2 8Bc is symmetrical about the point P in FIG.

2. The width of the flection 28Bc is smaller than the inner diameter of the cylindrical portion 20c2 so that the flection 28Bc does not come into touch with inner peripheral surface of the cylindrical portion 20c2.

Referring to FIG. 2, on the outer peripheral surface of the shroud tube 18, a metal band 36 is fixed on the rear end, and a slider fitting 38 is secured on the metal band 36 by laser welding. The slider is fitting 38 is secured to the metal band 36 after carrying out the primary aligning of the arc tube unit with respect to the rear end surface of the slider fitting 38 as a reference plane in the state that the metal band 36 is engaged in the slider fitting 38.

The insulating plug unit 14 comprises an insulating plug 40, a terminal cap 42, a contact ring 44, and a base plate 46.

Referring to FIG. 2, the insulating plug 40 comprises a inner cylindrical portion 40a, an outer cylindrical portion 40b formed to be connected to the inner cylindrical portion 40a at the rear end portion, a bulkhead portion 40c for closing the rear end portion of the inner cylindrical portion 40a, a cylindrical flange portion 40d extending from the peripheral edge of the bulkhead portion 40c to the rear, a boss portion 40e projecting from the midpoint of the bulkhead portion 40c to the rear, and a ring portion 40f formed on the outer cylindrical portion 40b.

The boss portion 40e is provided with a lead passage hole 40g extending in the fore-and-aft direction. in the center thereof. While the diameter of the lead passage hole 40g is somewhat larger than the diameter of the lead 28B, the diameter of the rear end portion of the lead passage hole 40g is almost the same as the diameter of the lead 28B. The front surface of the bulkhead 40c tapers toward the lead passage hole 40g.

Between the inner cylindrical portion 40a and the outer cylindrical portion 40b at the lower end portion of the insulating plug 40, there is provided an insertion hole 40h for inserting the L-shaped lead 32 and the rear end portion of the sleeve 34. At the rear end portion of the insertion hole 40h, there is formed a passage hole 40i for passing the rear end portion of the L-shaped lead 32 therethrough.

The terminal cap 42 is a terminal fitting comprising the plus terminal of the discharge bulb and press fitted to the boss portion 40e of the insulating plug 40 from the rear. Formed at the end portion of the terminal cap 42 is a lead passage hole 42a for passing the distal end portion 28Bb of the lead 28B. The hole 42a has almost the same diameter as the lead 28B therethrough. The lead 28B and the terminal cap 42 are secured with each other around the lead passage hole 42a by laser welding The contact ring 44 is a terminal fitting comprising the'minus terminal of the discharge bulb and secured on the outer peripheral surface of the bulkhead portion 40c of the insulating plug 40. on the contact ring 44, the rear end portion of the L shaped lead 32 is secured by laser welding.

The base plate 46 is fixed on the front-end portion of the inner cylindrical portion 40a of the insulating plug 40. On the base plate 46, a slider fitting 38 mounted on the arc tube unit 12 is secured by laser welding. At this time, the base plate 46 abuts the slider fitting 38 in plane-to-plane contact, and thus the secondary aligning of the arc tube unit 12 may be carried out before securing.

FIGS. 3(a)-3(c) illustrate a process to assemble an arc tube unit 12 to an insulating plug unit 14.

As shown in FIG. 3 (a), the arc tub.e unit 12 is brought close to the insulating plug unit 14 from the front side (though it is 'upper side" in the actual process for manufacturing discharge bulbs, it. is referred to as 'front side" throughout the description because it is 'front side" when the complete discharge bulb 10 is in normal use). The distal end portion 28Bb of the lead 28B is passed, through the lead passage hole 40g formed on the insulating plug 40, and then the slider fitting 38 -is brought into contact with the base plate 46.

At the time when the slider f itting 38 is brought into contact with the base plate 46, as shown in FIG.

3 (b), the distal end portion 28Bb of the lead 28B - 15 - protrudes through the lead passage hole 40g formed on the insulating plug 40 and the lead passage hole 42a formed on the terminal cap 42 toward the rear.

In this state, a laser beam from YAG laser 2 irradiates the slider fitting 38 to weld the slider fitting 38 to the base plate 46.

Next, the distal end portion 28Bb of the lead 28B protruding from the rear is cut off and, as shown in FIG. 3 (c), a laser beam from YAG laser 2 irradiates to the lead passage hole 42a formed on the terminal cap 42 to weld the distal end portion 28Bb of the lead 28B to the terminal cap 42.

In the process described above, in order to achieve the assembly of the arc tube unit 12 to the insulating plug unit 14 smoothly, it is essential to ensure that, in the process shown in FIG. 3(a), the distal end portion 28Bb of the lead 28B is passed through the lead passage hole 40g formed on the insulating plug 40 without fail.

In this respect, according to the present embodiment, a molybdenum wire used here to compose the lead 28B is annealed to possess an expansion property of 5% to 25%. The flection formed on the lead 28B is of a po intsymmetrical configuration, so that the distal end portion 28Bb of the lead 28B will pass through the lead passage hole 40g formed on the insulating plug 40.

The f lection. 2 8Bc of lead 2 8B is as shown in FIGS.

4 (a) -4 (c). A prescribed length of a molybdenum wire M is crimped by a pair of metal molds 4, 6 from both sides and undergoes a bending process. The flection 28Bc of resultant lead 28B formed in this way is subject to deformation from the initial configuration (configuration of metal molds) FIG. 5(a) illustrates a state of the lead 28B deformed by spring back action. A phantom line shows the initial. configuration and a solid line shows the configuration deformed by the spring back action.

As shown in FIGS. 4(a)-4(c), the extent of the spring back action is small. It is because a molybdenum wire M used in this embodiment has been annealed to possess an expansion property of 5% to 25%, and thus the spring back action can be reduced in comparison with the case where a wire which is not annealed is used. Suppression of the spring back action itself can be achieved only by setting an expansion property to 5% or higher. However, by setting an expansion property to 25% or lower, embrittlement of the wire due to recrystallization that occurred during annealing is prevented. This prevents breakage of the molybdenum wire M during subsequent bending process.

In the present embodiment, as shown in FIGS. 4(a)-4(c), since the flection 28Bc is symmetrical about the point P, even when the flection 28bc is subjected to deformation, it will be deformed almost point-symmetrically. Therefore, deformations in both ends of the lead 28B are almost compensated, and a displacement of the distal end portion 28Bb with respect to the axis of the proximal end portion 28Ba will be of little importance as shown in FIG. 5 (b).

On the other hand, as in the case of the lead 128B shown in FIG. 5 (c), when the f lection 128Bc is not point- symmetrical, deformations in both ends of the lead 28B cannot be compensated, and a displacement of the distal end portion 28Bb with respect to the axis of the proximal end portion 28Ba will be significant. The reason why the extent of spring back itself is large in FIG. 5(c) is because it is an example showing the case where an annealed molybdenum wire as in this embodiment is not used.

In the present embodiment, a displacement of the distal end portion 28Bb with respect to the proximal end portion 28Ba is of little importance as shown in FIG. 5 (b). There is no probability that the distal end portion 28Bb of the lead 28B swerves off the lead passage hole 40g formed on the insulating plug 40.

Therefore the distal end portion 28Bb of the lead 28B may be passed through the lead passage hole 40g formed on the insulating plug 40 without fail in the step shown in FIG. 3 (a) In addition, since a displacement of the distal end portion 28Bb with respect to the proximal end portion 28Bb may be kept in very small, the electrode assembly 22B can be inserted into the quartz glass tube (which is to be the arc tube body 20) easily to pinch-seal the electrode assembly 22B in the pinch seal portion 20b2 of the arc tube body 20.

As described in detail so far, a discharge bulb according to the present invention is provided with a flection between the rear pinch seal portion 20b2 and the distal end portion 28Bb of the lead 28B - 19 extending from the rear pinch seal portion20b2 toward the rear of the discharge bulb 10. Even when the lead 28B is subjected to thermal deformation due to on and off operation of the discharge bulb 10, the resultant expansion or contraction of the lead 28B can be absorbed by the deformations of the flection 28Bc, thus preventing a substantial thermal stress from being exerted on the lead 28B. Therefore, the probability that the lead 28B is damaged by a thermal stress and resulting in a failed discharge bulb 10 may be prevented.

According to the present embodiment, bending a wire that is annealed to possess an expansion property of 5% to 25% forms the flection 28Bc. The flection 28Bc is formed in a point-symmetrical configuration, and changes in the axial direction of the lead 28B between the proximal end portion 28Ba and the distal end portion 28Bb caused by spring back action may be effectively prevented. Therefore, the distal end portion 28Bb of the lead 28B can be passed through the lead passage hole 40g formed on the insulating plug 40 easily.

Since the directions of axis of the lead 28B - 20 between the proximal end portion 28Ba and the distal end portion 28Bb are almost identical, the electrode assembly 22B may be inserted into a quartz glass tube (which is to be the arc tube body 20) easily to pinch-seal the electrode assembly 22B to the pinch seal portion 20b2 of the arc tube body 20.

Whi.le the configuration of the flection 28Bc of the lead 28B is maintained in a zigzag shape by bending a wire during manufacturing process of the discharge bulb 10 in the present embodiment, it is also possible to deform the configuration of the flection 28Bc during the manufacturing process.

For example, a deformation as shown in FIGS.

6(a)-6(b) is also possible.

In other word, as shown in FIG. 6 (a), the flection 28Bc of the lead 28B is configured so as to come in contact with the inner peripheral surface of the cylindrical portion 20c2 of the arc tube body 20 in the stage before the arc tube unit 12 is assembled into the insulating plug unit 14. Subsequently, as shown in FIG. 6 (b), after the slider fitting 38 mounted on the arc tube unit 12 is secured to the base plate 46 on the insulating plug unit 14 by laser 21 - welding, the flection 28Bc is expanded to some extent by applying a tensile load toward the rear onto the distal end portion 28Bb of the lead 28B so that the flection 28Bc is brought out of contact with the inner peripheral surface of the cylindrical portion 20c2.

Then the distal end portion 28Bb of the lead 28B projecting from the rear is cut off, and the distal end portion 28Bb of the lead 28B is secured to the terminal cap 42 by laser welding.

10. In this way, by deforming the configuration of the f lection 22 8Bc during manufacturing process, the flection 28Bc of the lead 28B may be maintained in contact with the inner peripheral surface of the cylindrical portion 20c2 in the stage before assembling the arc tube unit 12 and the insulating plug unit 14. The electrode assembly 22B may be secured temporarily in the state of being registered with respect to the arc tube body 20 by the use of flection 29Bc when pinch-sealing the electrode assembly 22B on the rear side in the arc tube body 20. On the other hand, in the completed discharge bulb 10, the flection 28Bc is out of contact with the inner peripheral surface of the cylindrical portion 20c2. Therefore the flection 28Bc may reserve a margin for deformations required for absorbing expansion or contraction of the lead 28B caused by a thermal deformation of the. lead 28B.

While the arc tube body 20 is secured to the insulating plug 40 via a shroud tube 18 in the present embodiment, it is to be understood that the arc tube body 20 may be secured directly to the insulating plug 40.

is

Claims

1. A discharge bulb comprising:

an arc tube including an arc tube body extending in the fore-and-aft direction and a lead extending from a rear pinch seal portion situated at the rear end of the arc tube body; an insulating plug provided at the front end thereof with a securing portion for securing said arc tube body and at the rear end thereof with a lead passage hole for passing said lead therethrough; and a terminal cap mounted at the rear end of the insulating plug for securing the distal end portion of said lead, wherein there is a f lection in the intermediate region of said lead between said rear pinch seal portion and said distal end portion.

2. The discharge bulb according to claim 1, wherein said flection is point-symmetric.

3. The discharge bulb according to claim 1 or 2, wherein said lead is composed of a molybdenum wire which is annealed so as to possess an expansion property in the range of five percent to twenty- five percent.

4. The discharge bulb according to any preceding claim, wherein said flection is in a zigzag configuration.

5. The discharge bulb according to any one of claims 1 to 3, wherein said flection has a helical or spiral configuration.

6. A discharge bulb substantially as described with reference to Figures 1 to 6 of the accanpanying drawings.

7. A method of assembling an arc tube to an insulating plug, said arc tube including an arc tube body, with a lead extending from a rear pinch seal portion situated at the rear end of said arc tube body, said lead including-a flection, the method comprising:

inserting said lead through a terminal cap on said insulating plug unit; applying a tensile load to a distal end portion of said lead, thereby expanding said flection of said lead in the direction in which said tensile load is applied; securing said distal end portion of said lead to said terminal cap.

8. The method of assembly according to claim 7, further comprising a step of removing any portion of said distal end portion that projects from said terminal cap.

9. The method of assembly according to claim 7 or 8, wherein the step of securing said distal end portion of said lead to said terminal cap includes laser welding.

10. A method of assembling an arc tube substantially as described with reference to Figures 1 to 6 of the acconmanying drawings.

11. An arc tube comprising: an arc tube body and a lead extending from a rear pinch seal portion situated at the rear end of the arc tube body; and a flection formed by crimping an intermediate region of said lead between said rear pinch seal portion and a distal end portion thereof.

12. An arc tube according to claim 11, wherein said flection is formed in a zigzag configuration.

13. An arc tube according to claim 11, wherein said flection is formed in a helical r L ,)r spiral. configuratJon.

26 -

14. An arc tube according to any one of claims 11 t-o, 13, wherein said flection is point -symmetrical -

15. An arc tube according to any one of claims 11 to 14, wherein said flection is formed by crimping between metal molds.

16. An arc tube substantially as described with reference to Figures 1 to 6 of the accompanying drawings.

- 27