Automotive lamp bulb

Abstract: An automotive lamp bulb (1) is characterized in that the tip (upper end) of a common lead wire (9) is secured in the neck portion (15) of a glass bulb (2) with the aid of a bead (10). The low bead makes it possible to shorten the protruding upper portion of the glass bulb. The use of the bead makes it easier to align the lead wire with the neck portion. Because a bead is interposed, the lead wire is allowed to move in relation to the glass bulb, making it possible to use inexpensive hard glass. Consequently, an inexpensive and compact lamp bulb can be easily manufactured. This provides an automotive lamp bulb that is easy to process and that has a short projection in its upper part.

Description: The present invention relates to an improvement in an automotive lamp bulb. Japanese Laid-Open Utility Model Application 4-81349 ("Halogen Lamp Bulb") describes an example of a technique related to automotive lamp bulbs. The support wire 1 provided with a depression 3 and depicted in Figure 1 of the aforementioned application is prepared, a glass tube 2 is attached to the tip of the support wire 1 (Figure 2), and the glass tube 2 is heated and coated in this state. Figure 3 depicts the glass tube 2 after it has been bonded to the support wire 1. Figures 5 and 6 of the aforementioned application are reproduced here to provide a better description. Figures 6a and 6b are diagrams of the process for manufacturing a conventional halogen lamp bulb. Figure 6a corresponds to Figure 5 in the aforementioned application, and Figure 6b corresponds to Figure 6, but different symbols are used. In Figure 6a, a support wire 102 equipped with a glass tube 101 is inserted into a sealed glass body 103, the air is exhausted, and the assembly is heated. In the process, the exhausted gas or a halogen gas passes through a cylindrical conduit 104. Figure 6b, which is a diagram of the completed assembly, depicts a state in which the tip has been sealed by being softened and closed up with the aid of a burner. In Figure 6a, the passage resistance of the cylindrical conduit 104 is considerable because the glass tube 101 is long. The reason is that the passage resistance is directly proportional to the length and inversely proportional to the square of the cross-sectional surface area of the passage. In view of this, the clearance must be enlarged in order to lower the resistance. An enlarged clearance increases the diameter of the sealed glass body 103. Considerable time is needed to reduce the large-diameter sealed glass body 103 to the shape shown in Figure 6b. To obtain a uniform clearance, it is necessary to align the center of the support wire 102 with the center of the sealed glass body 103, and an advanced technique is needed to achieve such centering. Specifically, the technique described above involves complex processing and entails high processing costs. Another feature is that because of the considerable length of the glass tube 101 in Figure 6b above, the projection length H1 of the sealed glass body 103 is inevitably increased, contributing to the bulkiness of the halogen lamp bulb. In view of the foregoing, an object of the present invention is to provide an automotive lamp bulb that is easy to process and that has a short projection in its upper part. Aimed at addressing the aforementioned problems, Claim 1 pertains to an automotive lamp bulb wherein the opening of a glass bulb is sealed with the aid of a base, and at least one beam filament and at least two lead wires for supplying power to this beam filament are housed together inside this glass bulb, wherein a distinctive feature is that one of the aforementioned lead wires is extended, and the tip thereof is secured in the neck portion at the tip of the glass bulb with the aid of a bead. The low bead makes it possible to shorten the protruding upper portion of the glass bulb. Because the bead is merely in linear contact with the inner surface of the neck portion, a vent conduit can be formed, allowing exhausting and gas filling to be performed at a high rate. The use of the bead makes it easier to align the lead wire with the neck portion. Because a bead is interposed, the lead wire is allowed to move in relation to the glass bulb, making it possible to use inexpensive hard glass. Consequently, an inexpensive and compact lamp bulb can be easily manufactured. Claim 2 is characterized by the fact that a securing protrusion for securing the bead is provided in the upper portion of the aforementioned extended lead wire. The bead can be positioned on the lead wire with high precision, making manufacturing easier. Claim 3 is characterized by the fact that vent conduits are formed in the aforementioned bead. Large vent conduits can be secured, making it possible to perform exhausting and gas filling in a short time. Claim 4 is characterized by the fact that the vent conduits are depressions formed on the outer periphery of the bead or clearances formed between flat surfaces and the inner surface of the neck portion. Exhausting and gas filling can be accomplished in a short time because large vent conduits can be secured, and any cost increase can be prevented because the depressions or flat surfaces can be formed in a simple manner. Claim 5 is characterized by the fact that the vent conduits are clearances formed between the lead wire and the depressions formed on the inner periphery of the bead. Exhausting and gas filling can be accomplished in a short time because large vent conduits can be secured, and any cost increase can be prevented because the depressions or flat surfaces can be formed in a simple manner. Embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 is a diagram of the completed automotive lamp bulb pertaining to the present invention, Figure 2 is a diagram depicting the upper support structure of the automotive lamp bulb pertaining to the present invention, Figure 3 is a cross section of Figure 2 along line 3-3, Figure 4 is a diagram illustrating the manufacture of an automotive lamp bulb, Figure 5 is a modified example of the bead pertaining to the present invention, and Figure 6 is a diagram of the process for manufacturing a conventional halogen lamp bulb. In Figure 1, which is a diagram of the completed automotive lamp bulb pertaining to the present invention, the automotive lamp bulb 1 is a special lamp bulb in which the opening of a glass bulb 2 is sealed with the aid of a base 3; and inside glass bulb 2, a high-beam filament 4, a high-beam lead wire 5, a low-beam filament 6, a low-beam lead wire 7, a shield 8, and a common lead wire 9 are housed together; and a halogen gas is sealed inside. A structural feature is that the tip (upper end) of the common lead wire 9 is secured in the glass bulb 2 with the aid of a bead 10. 11 is a bridge, that is, a glass member for securing the lead wires 5, 7, and 9. A suitable material for the aforementioned glass bulb 2 and bead 10 is the widely used glass called B 2 O 3 -containing borosilicate glass or hard glass. When selected, the high-beam filament 4 is lighted up via a circuit comprising, in the order indicated or in the reverse order, the lead wire 5, the high-beam filament 4, and the common lead wire 9. When the low-beam filament 6 is selected, it is lighted up via a circuit comprising, in the order indicated or in the reverse order, the lead wire 7, the low-beam filament 6, the shield 8, and the common lead wire 9. The main function of the shield 8 is to block part of the light emitted by the filament 6; because the shield is made of metal, it is connected to one end of the filament 6. In Figure 2, which is a diagram depicting the upper support structure of the automotive lamp bulb pertaining to the present invention, the common lead wire 9 is a molybdenum rod, a securing protrusion 12 is formed in the upper portion of the wire, a rectilinear portion 13 is formed on top thereof, a bead 10 is fitted over the rectilinear portion 13, and the outermost peripheral portion 14 of the bead 10 is pressed against the inner surface of the neck portion 15 of the glass bulb 2. Because it is a horizontal line, the outermost peripheral portion 14 of the bead 10 is pressed against the neck portion 15 of the glass bulb 10 while in linear contact with it. Because the bead 10 is very low, the projection height H2 of the neck portion 15 is small. Figure 3, which is a cross section of Figure 2 along line 3-3, depicts an example in which a vent depression 21 is formed on the outer periphery of the bead 10, and the clearance between the depression 21 and the neck portion 15 is used as a vent conduit 22. The main points of the process for manufacturing the automotive lamp bulb presented above will now be described. Figures 4a and 4b a diagrams illustrating the manufacture of the automotive lamp bulb. In Figure 4a, the bead 10 is attached to the upper portion of the common lead wire 9. Because the bead 10 is secured with the securing protrusion 12, the bead 10 is stably positioned in the direction of the height, and is thus easier to attach. In Figure 4b, the common lead wire 9 equipped with the bead 10 is inserted into the neck portion 15 of the glass bulb 2. The inside diameter of the neck portion 15 is slightly greater than the outside diameter of the bead 10. The air is exhausted, nitrogen gas or another inert gas is introduced instead, and the neck portion 15 is heated with burners 17 in the atmosphere of the inert gas. Halogen gas is then sealed inside in accordance with the gas sealing method described below. (1) The base portion (portion located at a distance from the neck portion 15) of the glass bulb 2 is forcibly cooled with liquid nitrogen or another coolant. (2) [The interior] is filled with a high-pressure halogen gas once the inert gas is thermally shrunk. (3) The neck portion 15 is closed up and sealed, yielding the shape shown in Figure 2. In (1) above, the base portion is also cooled with the aid of the common lead wire 9. Because the common lead wire 9 is made of metal and has a higher thermal conductivity than glass, the upper portion reaches a low temperature in a short time. The neck portion 15 is also partially cooled if the structure is such that the upper end of the common lead wire 9 is in direct contact with the neck portion 15. The glass bulb 2 does not pose any problems if it has a low coefficient of thermal expansion, can withstand thermal shocks, and is made of quartz glass. However, cracks are likely to develop in the neck portion 15 if the glass bulb 2 is made of hard glass, which has a higher coefficient of thermal expansion than quartz glass. In view of this, the temperature changes of the common lead wire 9 are reduced below those of the neck portion 15, and hard glass can be used because of the use of a structure in which a bead 10 with a low thermal conductivity is interposed between the upper portion of the common lead wire 9 and the neck portion 15, as in Figure 4b. Cases involving the use of hard glass and quartz glass are collated in Table 1 below. Forming a vent depression 21 in the bead 10 and securing a vent conduit 22 allow the exhausted gas or halogen gas to escape primarily through the vent conduit 22, making it possible to accomplish exhausting and gas sealing with high efficiency. It is also possible to use a bead 10 devoid of the vent depression 21. In this case, the clearance between the outermost peripheral portion 14 of the bead 10 and the inner peripheral surface of the neck portion 16 functions as a vent conduit. The reason is that, as described above, the bead 10 and the neck portion 15 are in linear contact with each other, with the result that the conduit is very short and the passage resistance low, ensuring a stable gas flow. Figures 5a through 5c are diagrams depicting a modified example of the bead pertaining to the present invention. In Figure 5a, flat surfaces 23 are formed on the outer periphery of a bead 10B, thin half-moon clearances are formed between the flat surfaces 23 and the inner surface of the neck portion 15, and these clearances function as vent conduits 22. As used herein, the term "flat surface" refers to a flat surface obtained by cutting off a portion of a round bar. The flat surface can also be formed by press molding. In Figure 5b, flat surfaces 24 are formed on the outer periphery of a bead 10C, thin half-moon clearances are formed between the neck portion 15 and the flat surfaces 24, and these clearances function as vent conduits 22. In Figure 5c, a plurality of vent depressions 25 are formed on the inner periphery of a bead 10D. Next, the "hard glass" adopted in the practical examples under consideration and the "quartz glass" adopted for some halogen lamp bulbs will be compared with reference to Table 1. Practical Example Comparative Example Name Hard glass Quartz glass Reference components SiO 2 56% At least 96% B 2 O 3 5% At least 3.5% Al 2 O 3 16% At least 0.3% Other 23% Less than 0.2% Softening point 926°C 1530°C Coefficient of thermal expansion 44 × 10 -7 /°C 7.5 × 10 -7 /°C Cost Low High Quartz glass, which is cited in the "Comparative Example" column, essentially consists of silica, finds additional uses in high-grade test tubes and electric-heater coating glass, and is highly resistant to thermal shocks. As is shown in the table, this material has a high softening point (1530°C), good heat resistance, and a low coefficient of thermal expansion, and, as a result, develops high thermal strength. A drawback is the high cost. Using this quartz glass makes it possible to bond the tip of the common lead wire 9 directly to the glass bulb 2. The reason is that the glass bulb 2 does not break even when the axial force (generated by thermal expansion) of the common lead wire 9 is exerted. On the other hand, quartz glass has a high softening point, so the glass bulb 2 whose neck portion 15 is to be sealed must be heated to a high temperature. Hard glass, which is cited in the "Practical Example" column, has low silica purity and is therefore inexpensive, but the softening point is 926°C, and the hot strength is considerably lower than that of quartz glass. In view of this, the common lead wire 9 is secured in the glass bulb 2 with the aid of the bead 10, as shown in Figure 2. It is expected that the glass bulb 2 and the outer periphery of the bead 10, or the bead 10 and the common lead wire 9, will slide in relation to each other. Such sliding prevents excessive force from being exerted on the glass bulb 2. The low softening point makes it possible to seal the glass bulb 2 at a comparative low temperature. Consequently, adopting the structure of the practical example makes it possible to use the inexpensive hard glass and makes it very easy to manufacture a product. The number and shape of the vent conduits 22 formed in the bead 10 are not limited by the practical example. In addition, the practical example involved extending the common lead wire 9, but this arrangement is not the only option. It is also possible to extend the lead wire 5 of the high-beam filament or the lead wire 7 of the low-beam filament. In addition, the securing protrusion 12 can be formed on the common lead wire 9 by pressure bending, or it can be formed by depositing a chip on the common lead wire 9. An automotive lamp bulb 1 is characterized in that the tip (upper end) of a common lead wire 9 is secured in the neck portion 15 of a glass bulb 2 with the aid of a bead 10. The low bead makes it possible to shorten the protruding upper portion of the glass bulb. The use of the bead makes it easier to align the lead wire with the neck portion. Because a bead is interposed, the lead wire is allowed to move in relation to the glass bulb, making it possible to use inexpensive hard glass. Consequently, an inexpensive and compact lamp bulb can be easily manufactured. This provides an automotive lamp bulb that is easy to process and that has a short projection in its upper part.

Claims: An automotive lamp bulb (1), wherein the opening of a glass bulb (2) is sealed with the aid of a base (3) and at least one beam filament (4,6) and at least two lead wires (5,7,9) for supplying power to this beam filament (4,6) are housed together inside this glass bulb (2), wherein said automotive lamp bulb (1) is characterized in that one (9) of the aforementioned lead wires (5,7,9) is extended, and the tip thereof is secured in the neck portion (15) at the tip of the glass bulb (2) with the aid of a bead (10). An automotive lamp bulb as defined in Claim 1, characterized in that a securing protrusion (12) for securing the bead (10) is provided in the upper portion of the aforementioned extended lead wire (9). An automotive lamp bulb as defined in Claim 1 or 2, characterized in that vent conduits (22) are formed in the aforementioned bead (10). An automotive lamp bulb as defined in Claim 3, characterized in that the aforementioned vent conduits (22) are depressions formed on the outer periphery of the bead (10B,10C) or clearances formed between flat surfaces (23,28) and the inner surface of the aforementioned neck portion (15). An automotive lamp bulb as defined in Claim 3, characterized in that the aforementioned vent conduits (22) are clearances formed between the aforementioned lead wire (9) and the depression (25) formed on the inner periphery of the bead (10D).

Inventors: HASEGAWA TORU, TABATA HAJIME, HASEGAWA, TORU, TABATA, HAJIME
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1997
Main classification: H01K1
IPC codes: H01K1, H01K9