JP7765307B2 - discharge lamp - Google Patents

Description

The present invention relates to discharge lamps such as short arc discharge lamps, and in particular to heat dissipation from electrodes.

When a discharge lamp is lit, the electrode tip becomes very hot, causing the electrode material, such as tungsten, to melt and evaporate, blackening the discharge tube and reducing the lamp's illuminance. To prevent the electrode, including the electrode tip, from overheating, a known structure is one in which a heat conductor, such as a metal, is enclosed inside the electrode (see Patent Document 1). In this structure, a heat conductor made of a metal with high thermal conductivity and a relatively low melting point, such as silver, is sealed inside the anode. As the electrode temperature rises when the lamp is lit, the heat conductor melts and liquefies. This causes thermal convection within the enclosed space, and heat from the electrode tip is transported to the electrode support rod on the opposite side.

Other known configurations include a configuration in which a plate-shaped member (flow regulator) that forms a flow path along the electrode axis is placed within the sealed space to promote thermal convection (see Patent Document 2), and a configuration in which a plate-shaped member (regulator) that restricts the circumferential flow of the molten heat transfer material is placed within the sealed space to prevent high-temperature creep deformation caused by temperature differences within the sealed space due to thermal convection in the heat transfer material (see Patent Document 3).

Japanese Patent Application Laid-Open No. 2004-006246 Patent No. 6259450 JP 2012-028168 A

When the lamp is turned on, the flow of molten heat transfer material acts on the flow rectifier, etc., causing it to tilt in some cases. When the flow rectifier, etc. tilts, there is a temperature difference between the bottom and ceiling sides of the sealed space, and the amount of thermal expansion of the flow rectifier, etc. varies along the electrode axis. This causes deformation such as warping, which may lead to cracks or damage to the flow rectifier, etc.

Therefore, it is necessary to prevent cracks from occurring in electrodes, such as flow regulators, which are placed in a sealed space that encloses a heat transfer material.

A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube. At least one of the electrodes forms an enclosed space in which a heat transfer material that melts when the lamp is lit is sealed, and a plate-shaped flow rectifier is arranged within the enclosed space.

The "flow regulator" here refers to a component that can adjust the flow of a heat transfer material within an enclosed space, such as by forming a flow path, guiding the flow direction, or promoting flow. The flow regulator is composed of multiple components, and can be configured, for example, by stacking multiple plate-shaped components. Furthermore, "plate-shaped" means that the flow regulator can be configured as a plate-shaped component overall, and can also be configured as a flow regulator with an external shape that combines multiple plate-shaped components, such as a T-shape or cross-shape. The multiple plate-shaped components can be configured by solid-state welding together.

In the present invention, in the flow rectifier, the plate-shaped member constituting one side (herein referred to as the first plate-shaped member) is thicker than the plate-shaped member constituting the other side (herein referred to as the second plate-shaped member). Here, "one side" refers to the side facing the electrode tip when the flow rectifier is tilted within the sealed space when the lamp is lit, and "the other side" refers to the opposite side, or the side facing away from the electrode tip. The first plate-shaped member and the second plate-shaped member each constitute such a side.

In another aspect of the discharge lamp of the present invention, the flow rectifier is configured so that the first plate-shaped member constituting one side has a smaller thermal expansion coefficient than the second plate-shaped member constituting the other side.

In a discharge lamp according to another aspect of the present invention, the plate-shaped rectifier is composed of one member or multiple members. For example, a one-piece member with an external shape such as a T-shape or a cross, formed by cutting, is also included as a plate-shaped rectifier. Furthermore, when the lamp is lit, the rectifier is tilted within the sealed space, and the difference in the amount of thermal expansion along one side and the other side is suppressed.

The present invention makes it possible to suppress the occurrence of cracks in electrodes, such as flow regulators, placed in a sealed space that encloses a heat transfer material.

1 is a plan view of a discharge lamp according to an embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of an anode. 3 is a schematic cross-sectional view taken along line III-III in FIG. 2. FIG. 2 is a cross-sectional view of the flow regulator taken along the longitudinal direction. FIG. 10 is a diagram showing a state in which the flow regulator is tilted. FIG. 10 is a schematic cross-sectional view of a flow rectifier for a discharge lamp according to a second embodiment.

The short arc discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light. It has a roughly spherical discharge tube (light-emitting tube) 12 made of transparent quartz glass. A pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially) within the discharge tube 12. On either side of the discharge tube 12, quartz glass sealing tubes 13A, 13B are connected to and integrally formed with the discharge tube 12. Mercury and rare gases such as halogen and argon gas are sealed in the discharge space DS within the discharge tube 12.

Electrode 20, which serves as the cathode, is supported by electrode support rod 17A. Sealed within sealed tube 13A are a glass tube (not shown) through which electrode support rod 17A is inserted, lead rod 15A that connects to an external power source, and metal foil 16A that connects electrode support rod 17A to lead rod 15A. Similarly, electrode 30, which serves as the anode, is sealed with mounting parts such as a glass tube (not shown) through which electrode support rod 17B is inserted, metal foil 16B, and lead rod 15B. Furthermore, caps 19A and 19B are attached to the ends of sealed tubes 13A and 13B, respectively.

When a voltage is applied to the pair of electrodes 20, 30, an arc discharge occurs between the electrodes 20, 30, and light is emitted toward the outside of the discharge tube 12. A power of 1 kW or more is applied here. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

Figure 2 is a schematic cross-sectional view of the electrode (anode) 30. Figure 3 is a schematic cross-sectional view taken along line III-III in Figure 2.

As shown in Figure 2, the anode 30 is composed of a cylindrical body 34 and a truncated cone-shaped tip 32 having an electrode tip surface 30S. The body 34 has a structure in which a sealing lid 60, to which an electrode support rod 17B is attached, is joined. In this example, the body 34 and tip 32, excluding the sealing lid 60, are molded from the same metal material, such as tungsten. However, they may also be molded from different materials. The sealing lid 60 may also be molded from the same metal material, such as tungsten.

A cylindrical sealed space 50 is formed in the center of the interior of the body 34, coaxially with the electrode axis E. A heat transfer material M is sealed in the sealed space 50. The heat transfer material M is made of a metal (e.g., silver) with a lower melting point than the body 34 and the sealing lid 60. When the lamp is lit, it melts into a liquid and convects within the sealed space 50. Figure 2 shows the molten heat transfer material M convecting. Here, the heat transfer material M is sealed in such a way that the entire flow rectifier 40 is immersed in the molten state (when the lamp is lit).

A flow regulator 40 is disposed in the sealed space 50. In this case, the flow regulator 40 is made of a high-melting-point metal (such as tungsten, molybdenum, or tantalum) or an alloy with potassium additive, and is configured as a plate-shaped member with the function (structure) of promoting convection in the heat transfer body M.

Specifically, the flow straightener 40 is not sized or shaped to restrict convection in the vertical, horizontal, or circumferential directions (the entire circumference) of the sealed space 50. The distance D1 between the upper end 40T of the flow straightener 40 and the ceiling surface 50T of the sealed space 50, the distance D2 between the lower end 40D and the bottom surface 50B, and the distance D3 between the side surface 50S of the sealed space along the direction perpendicular to the electrode axis of the sealed space 50 are ensured to allow the heat transfer material M to flow along the side surfaces 40S1 and 40S2 of the flow straightener 40, and overflow the upper end 40T and lower end 40D of the flow straightener 40. The flow straightener 40 may be placed in the sealed space 50, in which case the distance D2 is essentially eliminated.

Furthermore, the flow rectifier 40 is positioned so that its central axis is aligned near the electrode axis E. However, when the heat transfer material M is molten (the lamp is lit), the position of the flow rectifier 40 is not fixed. For this reason, the flow rectifier 40 is not shown hatched in Figure 2 for convenience.

Figure 4 is a cross-sectional view of the flow straightener 40 along its longitudinal direction. Figure 5 is a diagram showing the flow straightener 40 in an inclined state. The configuration of the flow straightener 40 in this embodiment will be explained using Figures 4 and 5. However, in Figure 5, the inclination of the flow straightener 40 is exaggerated.

The rectangular flow regulator 40 here has a structure in which two plate-shaped members 40A and 40B (hereinafter referred to as the first plate-shaped member and the second plate-shaped member) are stacked and joined (by welding, solid-state welding, etc.). The first and second plate-shaped members 40A and 40B are configured to have the same size (area), and can be configured, for example, with a longitudinal length L of approximately 30 mm and an overall thickness T of approximately 1 mm. Furthermore, the first and second plate-shaped members 40A and 40B are made of the same material (tungsten in this case).

On the other hand, the thicknesses T1 and T2 of the first and second plate-shaped members 40A and 40B are different, with the first plate-shaped member 40A being thicker than the second plate-shaped member 40B (T1 > T2). Here, the thickness T1 of the first plate-shaped member 40A is set within the range of 1.1 to 2.0 times the thickness T2 of the second plate-shaped member.

In this way, the flow regulator 40 has a structure in which first and second plate-like members 40A and 40B of different thicknesses are stacked together, which, as will be explained below, can prevent cracks from occurring in the flow regulator 40 when the lamp is tilted while it is lit.

When the lamp is lit, if the rectifier 40 tilts with the side surface 40S1 of the first plate-shaped member 40A toward the electrode tip, which is relatively hot, the first plate-shaped member 40A is closer to the bottom surface 50B of the sealed space 50 and therefore receives a greater amount of heat than the second plate-shaped member 40B, which is closer to the ceiling surface 50T of the sealed space 50. If we consider the temperature of the entire rectifier 40 to rise, a temperature difference will occur between the first plate-shaped member 40A and the second plate-shaped member 40B.

However, the thermal capacity between the first plate-shaped member 40A and the second plate-shaped member 40B of the flow regulator 40 differs due to the difference between the thicknesses T1 and T2. Therefore, the amount by which the first plate-shaped member 40A extends along its side surface 40S1 (longitudinal direction) due to thermal expansion (hereinafter referred to as the thermal expansion amount) is approximately equal to the amount of thermal expansion along the side surface 40S2 of the second plate-shaped member 40B. Alternatively, the difference in the amount of thermal expansion is suppressed. This is observed regardless of how the first plate-shaped member 40A and the second plate-shaped member 40B are joined.

This prevents the flow rectifier 40 from warping and cracking due to the difference in the amount of thermal expansion along the side surface of the electrode tip and the side surface of the electrode support rod when the flow rectifier 40 is tilted. As a result, the flow rectifier 40 can perform its function until the end of the lamp's life, and the lamp temperature can be suppressed.

When the flow straightener 40 tilts, the relatively heavy first plate-shaped member 40A tilts toward the electrode tip. To ensure this tilt, the thickness T2 of the second plate-shaped member 40B of the flow straightener 40 may be configured to be thinner on the ceiling surface side of the sealed space 50.

Next, we will explain the second embodiment of the discharge lamp using Figure 6. In the second embodiment, the flow rectifier is constructed by laminating materials with different thermal expansion coefficients.

Figure 6 is a schematic cross-sectional view of the rectifier of the discharge lamp of the second embodiment. The rectifier 240 has a structure in which a first plate-shaped member 240A and a second plate-shaped member 240B are overlapping and bonded together. The thicknesses T1 and T2 of the first plate-shaped member 240A and the second plate-shaped member 240B are equal, and the length L along the side is also equal.

On the other hand, the first plate-shaped member 240A is made of a different material from the second plate-shaped member 240B, and is made of a material with a smaller thermal expansion coefficient than the second plate-shaped member 240B. For example, the first plate-shaped member 240A is made of tungsten, and the second plate-shaped member 240B is made of molybdenum. Alternatively, the first plate-shaped member 240A may be made of tantalum, and the second plate-shaped member 240B may be made of titanium. When the flow rectifier 240 tilts, the first plate-shaped member 240A tilts toward the electrode tip.

By constructing the flow regulator 240 using the first plate-shaped member 240A and the second plate-shaped member 240B, which have different thermal expansion coefficients, it is possible to obtain the same effects as in the first embodiment. Furthermore, even if the flow regulator 240 tilts, the position of the flow regulator 240 or the weight of its constituent materials may be adjusted so that the first plate-shaped member 240A tilts toward the electrode tip.

In the first and second embodiments, the flow regulator is formed using two plate-like members, but it may also be formed using three or four or more stacked plate-like members. For example, in the first embodiment, it may be formed by stacking plate-like members of different thicknesses, or several plate-like members may be set to the same thickness and the thickness may become thinner in stages.

In addition, in the second embodiment, the plate-shaped members may be stacked so that the thermal expansion coefficient increases in stages, or several plate-shaped members with the same thermal expansion coefficient may be stacked on top of each other so that the thermal expansion coefficient increases in stages. For a flow rectifier that is tilted while the lamp is lit, the amount of thermal expansion along one of the opposing side surfaces (surfaces) should be configured to be approximately equal to the amount of thermal expansion along the other side surface, or the difference in thermal expansion should be suppressed.

The above describes a flow regulator that promotes convection in the heat transfer body M, but the flow regulator may also be configured as a component that partially regulates flow, such as regulating the flow in the circumferential direction of the heat transfer body M. For example, a plate-shaped flow regulator with a cross-shaped or T-shaped cross section can be configured. The thickness and thermal expansion coefficient of the portion that slopes toward the tip of the electrode, which becomes relatively hot, can then be adjusted to reduce the difference in thermal expansion with other portions.

For example, when constructing a flow straightener with a T-shaped cross section, it is constructed from a first plate-shaped member corresponding to the vertical bar portion of the T, and a second plate-shaped member corresponding to the horizontal bar portion of the T. In this case, the first plate-shaped member constitutes one side of the T-shaped cross section flow straightener, and the second plate-shaped member constitutes one side of the T-shaped cross section flow straightener.

In consideration of the state in which the flow regulator tilts within the sealed space, it is possible to configure the first plate-shaped member to be thicker than the second plate-shaped member, or to configure the first plate-shaped member with a smaller thermal expansion coefficient than the second plate-shaped member. Regarding a flow regulator with a T-shaped cross section, the first plate-shaped member and the second plate-shaped member can be fitted together or joined together, but it is also possible to change the thickness by cutting or other processes to create a cross-shaped or T-shaped cross section.

10 Discharge lamp 30 Electrode (anode)
40 Flow regulator 40A First plate-like member 40B Second plate-like member 50 Sealed space

Claims (4)

A discharge tube;
a pair of electrodes disposed opposite each other within the discharge tube;
At least one of the electrodes has a sealed space formed therein in which a heat transfer material that melts when the lamp is lit is sealed, and a plate-shaped flow rectifier is disposed in the sealed space;
In the flow rectifier, the first plate-like member constituting one side surface is thicker than the second plate-like member constituting the other side surface. A discharge tube;
a pair of electrodes disposed opposite each other within the discharge tube;
At least one of the electrodes has a sealed space formed therein in which a heat transfer material that melts when the lamp is lit is sealed, and a plate-shaped flow rectifier is disposed in the sealed space;
In the flow rectifier, the first plate-like member constituting one side surface has a smaller thermal expansion coefficient than the second plate-like member constituting the other side surface. A discharge lamp as described in claim 1 or 2, characterized in that the rectifier is made by stacking multiple plate-shaped members. A discharge lamp as described in claim 3, characterized in that the multiple plate-shaped members are solid-state welded to each other.