Single terminal type discharge lamp

Abstract: A single terminal type discharge lamp is provided, which comprises: a burner; a socket; a tubular holder, to which the burner is fitted, provided in the socket along a predetermined direction in which the burner is to be aligned; and a tubular metal holder spring which is mounted to the holder for radially depressing the holder toward the burner with deflecting force; wherein the burner is adhered to the socket due to the melt of the holder caused by the heat of the holder spring owing to radio-frequency heating which is performed when the one end of the burner is fitted to the holder such that the burner attains a predetermined position. Accordingly, the number of parts and the number of manufacturing steps are both reduced, thereby reducing costs of the discharge lamp.

Description: 1. Field of the Invention The present invention relates to a discharge lamp, and more particularly to a discharge lamp of a single terminal type at one end of which a base is provided for purposes of using it as a light source for a head lamp of an automobile or a light source for an LED projector. 2. Background Art One example of a prior single terminal type discharge lamp is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei.8-64114 corresponding to EP-A-0 696 046. In this prior discharge lamp, a burner is once attached to a self-core adjustment type holder member with a spherical outer surface, and then the holder member is inserted into a tubular socket. Thereafter the holder member and the socket are welded in a condition that the depth and the direction of the holder member are adjusted. However there are some problems for the above-described discharge lamp. First, the manufacturing costs of the discharge lamp increase, because the necessity of two members, the holder member and the socket, as the base makes the construction of the lamp complicated and the necessity of two attachment steps consisting of the attachment between the burner and the holder member and the attachment between the holder member and the socket increases the number of total manufacturing steps. Second, a dielectric strength of the discharge lamp against a high voltage required on turning on the discharge lamp is insufficient, because the distance between lead wires respectively connected to two electrodes of the discharge lamp is too small in the socket due to the necessity of two connecting spaces in the socket for attaching the burner to the holder member and attaching the holder member to the socket. Third, a mechanical strength between the holder member and the socket of the discharge lamp is also insufficient, because the welding area of the holder member and the socket is small due to a linear contact between the holder member with a spherical outer surface and the socket. Thus the holder member would separate from the socket due to vibrations or impacts on driving an automobile. SUMMARY OF THE INVENTION It is an object of the present invention to provide a single terminal type discharge lamp which can be manufactured with low costs and has a sufficient dielectric strength against a high voltage and a sufficient mechanical strength between the holder member and the socket. In order to achieve the foregoing object and others, the present invention provides a single terminal type discharge lamp comprising: a burner comprising a discharge tube and a covering tube; a thermoplastic socket attached to one end of the burner; a tubular holder, to which the burner is fitted, provided in the socket along a predetermined direction in which the burner is to be aligned; and a tubular metal holder spring which is mounted to the holder for radially depressing the holder toward the burner with deflecting force; wherein the burner is adhered to the socket due to the melt of the holder caused by the heat of the holder spring owing to radio-frequency heating which is performed when the one end of the burner is fitted to the holder such that the burner attains a predetermined position. Other features and advantages of the present invention will be apparent from the following description taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially exploded perspective view of a single terminal type discharge lamp of an embodiment according to the present invention. FIG. 2 is a sectional view taken along the line A-A of FIG. 1. FIG. 3 is a perspective view of the principal part of a single terminal type discharge lamp of an another embodiment according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, reference numeral 1 is a single terminal type discharge lamp of one embodiment according to the present invention. The single terminal type discharge lamp 1 is constructed such that a socket 3 made of a thermoplastic resin is attached by welding to one end of a burner 2 comprising a discharge tube 2a and a covering tube 2b, as well as the prior discharge lamp described above. In the present invention, the holder 4 made of a thermoplastic resin is formed at the inside of the socket 3 and integrated with the socket 3 in one piece. The holder 4 with a tubular shape is provided on the base 3a of the socket 3 along a predetermined direction in which the burner 2 is to be aligned such that the outer surface of the burner 2 faces the inner surface of the holder 4 when the burner 2 is fitted to the holder 4. A tubular holder spring 5 having a deflecting force toward a direction for reducing the diameter thereof made of a metal member comprising a predetermined amount of, e.g., wolfram as a resistance component with elasticity of an appropriate value such as steel alloy products or spring products is mounted to the holder 4 to cover the outer surface of the holder 4. The deflecting force of the holder spring 5 must not be so large, but it should be sufficient for reducing the diameter of the holder 4 in welding described later. Reference numeral 7 in the figures is a lead wire provided on both ends of the burner 2. Reference numeral 8 designates a ceramic plate for protecting the socket 3 from the heat of the burner 2 generated when it is turned on, and so on. Reference numeral 9 designates a ceramic tube for insulating the lead wire 7 on the opposite side of the socket 3. When the burner 2 is attached to the socket 3 formed as described above, one end of the burner 2 is inserted into the holder 4. In this case, since the holder 4 is provided in the socket 3 along the predetermined direction in which the burner is to be aligned, the central axis of the burner-2 is positioned at a designed position in the socket 3. Thus a discharge chamber 2c of the burner 2 can be placed at a predetermined position by adjusting the inserting depth of the burner 2 in the holder 4 on the basis of a flange 3b of the socket 3. On adjusting the inserting depth, the burner 2 can freely slide in the holder 4, because the holder spring does not have a deflecting force enough to deform the shape of the holder 4, but enough to reduce the diameter of the holder 4. After the discharge chamber 2c is placed at the predetermined position by such procedures, the socket 3 is subject to radio-frequency heating while the discharge chamber 2c is maintained at the position. Then the holder spring 5 is heated by dielectric heating. A part of the holder 4 directly contacting the holder spring 5 is also heated due to thermal conduction from the holder spring 5. The holder 4 made of the thermoplastic resin is softened and melted by the heating, and thus the diameter of the holder 4 is reduced by the deflecting force of the holder spring 5, thereby depressing the burner 2, allowing the burner 2 to be welded to the holder 4. After the radio-frequency heating is stopped at an appropriate timing, the holder 4 which is once softened and melted is again hardened, which in turn allows the burner 2 and the holder 4 to be fixed by welding. Next, effects of the single terminal type discharge lamp 1 of the present embodiment are described. First, since the discharge lamp 1 has a construction such that the holder 4 is provided on the base of the socket 3, it is possible to form the socket 3 and the holder 4 as an integrated body with the use of a mold or the like. Therefore, it is not necessary to provide the holder 4 as another parts, which in turn reducing the number of parts of the discharge lamp 1. It is also possible to reduce manufacturing steps, because a step for attaching the burner 2 to the holder 4 includes a step for attaching the burner 2 to the socket 3. Second, only one connecting part for attaching the burner 2 to the socket 3 is required in the socket 3, thereby reducing spaces for connections in the socket 3. Accordingly, it is possible to provide a large distance between lead wires respectively connected to two electrodes of the discharge lamp 1 in the socket, which in turn provides a sufficient dielectric strength against a high voltage on turning on the discharge lamp with the discharge lamp. Third, it is possible to obtain a sufficient mechanical strength between the burner 2 and the holder 4 or the socket 3 such that they are not separated even if, for example, vibrations or impacts are applied on driving an automobile, because the burner 2 is welded to the holder 4 or the socket 3 at a large area having a tubular shape. Another embodiment of the present invention is shown in FIG. 3. While the burner 2 is fitted to or inserted into the holder such that the outer surface of the burner 2 faces the inner surface of the holder 4 in the foregoing embodiment, in the present embodiment, the holder 4 is fitted to or inserted into the burner 2 such that the outer surface of the holder 4 faces the inner surface of the burner 2. In this case, a holder spring 6 has a deflecting force in a direction for increasing the diameter thereof or in a direction toward the burner 2. The holder spring 6 is mounted on the inner surface of the holder 4. Thus the holder 4 is welded to the burner 2 by radio-frequency heating while the diameter of the holder 4 increases due to the deflecting force of the holder spring 6. As described above, according to a single terminal type discharge lamp of the present invention comprising: a burner comprising a discharge tube and a covering tube; a thermoplastic socket attached to one end of the burner; a tubular holder, to which the burner is fitted, provided in the socket along a predetermined direction in which the burner is to be aligned; and a tubular metal holder spring which is mounted to the holder for radially depressing the holder toward the burner with deflecting force; wherein the burner-is adhered to the socket due to the melt of the holder caused by the heat of the holder spring owing to radio-frequency heating which is performed when the one end of the burner is fitted to the holder such that the burner attains a predetermined position, first, it is possible to reduce the number of parts of the discharge lamp and also the number of manufacturing steps, only one welding part being required in the present invention although two welding parts being required in the prior art, thereby providing an excellent effect for reducing costs of such a single terminal type discharge lamp. Second, only one connecting part for attaching the burner to the socket is required in the socket, thereby reducing spaces for connections in the socket. Accordingly, it is possible to provide a large distance between lead wires respectively connected to two electrodes of the discharge lamp in the socket, which in turn provides a sufficient dielectric strength against a high voltage on turning on the discharge lamp with the discharge lamp, thereby providing an excellent effect for increasing properties of the discharge lamp. Third, it is possible to obtain a sufficient mechanical strength between the burner and the holder or the socket such that they are not separated even if, for example, vibrations or impacts are applied on driving an automobile, because the burner is welded to the holder or the socket at a large area having a tubular shape, thereby providing an excellent effect for increasing reliability of the discharge lamp.

Claims: A single terminal type discharge lamp (1) comprising: a burner (2) comprising a discharge tube (2a) and a covering tube (2b); a thermoplastic socket (3) attached to one end of the burner (2); a tubular holder (4), to which the burner (2) is fitted, provided in the socket (3) along a predetermined direction in which the burner (2) is to be aligned; characterized in that the single terminal type discharge lamp (1) further comprises a tubular metal holder spring (5; 6) which is mounted to the holder (4) for radially depressing the holder (4) toward the burner (2) with deflecting force; wherein the burner (2) is adhered to the socket (3) due to the melt of the holder (4) caused by the heat of the holder spring (5; 6) owing to radio-frequency heating which is performed when the one end of the burner (2) is fitted to the holder (4) such that the burner (2) attains a predetermined position. A single terminal type discharge lamp according to claim 1, wherein the tubular holder (4) is integrally formed with the thermoplastic socket (3) in one piece. A single terminal type discharge lamp according to claim 1 or 2 wherein the fitting of the burner (2) to the holder (4) is such that the outer surface of the burner (2) faces the inner surface of the holder (4). A single terminal type discharge lamp according to claim 1 or 2 wherein the fitting to the burner (2) in the holder (4) is such that the inner surface of the burner (2) faces the outer surface of the holder (4).

Inventors: KUDO TETSUYA, SATO ISAMU, TSURUMARU AKIHIKO, KUDO, TETSUYA, SATO, ISAMU, TSURUMARU, AKIHIKO
Applicants: STANLEY ELECTRIC CO LTD, STANLEY ELECTRIC CO., LTD.
Application year: 1997
Main classification: H01J9
IPC codes: H01J5, H01J9