EP1974367B1 - High-pressure discharge lamp having cooling laminates fitted at the end of the discharge vessel - Google Patents

Description

Technical area

The invention relates to a high-pressure discharge lamp according to the preamble of claim 1. Such lamps are in particular high-pressure discharge lamps with a ceramic discharge vessel for general lighting. These are, in particular, metal halide lamps or else sodium high-pressure lamps or high-pressure mercury lamps.

State of the art

The US Pat. No. 4,970,431 respectively. EP 315 261 discloses a sodium high-pressure discharge lamp in which the bulb of the discharge vessel is made of ceramic. At the ends of the cylindrical discharge vessel fin-like extensions are attached, which serve the heat dissipation.

From the EP-A 506 182 are coatings of graphite or carbon or similar known, which are applied to ceramic discharge vessels at the ends to effect cooling.

The GB 2 281 148 , the JP-A 03-004436 and the JP-A 08-250071 describe discharge vessels made of quartz glass, which have unevennesses or outgrowths at various points for various reasons.

Presentation of the invention

The object of the present invention is to provide a high-pressure discharge lamp whose color spread is significantly reduced compared to previous lamps.

This object is achieved by the characterizing features of claim 1.

Particularly advantageous embodiments can be found in the dependent claims.

The high-pressure discharge lamp with a ceramic discharge vessel has a central part and two ends which are closed by tailpipes, wherein electrodes are anchored in the tailpipes, which extend into the discharge volume enveloped by the discharge vessel, wherein a filling containing metal halides or metals in the Discharge volume is housed. In this case, fin-like lamellae which extend radially outward are seated at the ends. It is the surface of the lamellae is generally arranged predominantly in a region which lies behind a line away from discharge, which is determined by the projection of the tip of the electrode onto the inner surface of the discharge vessel. The arrangement of the lamellae is preferably rotationally symmetrical to each other, in particular with a three- to eight-fold Symmetry. Here, for the sake of simplicity, the shape of the slats may be substantially similar, but need not. For example, two sets of lamellae may be alternately used, for an eightfold symmetry, four each of a kind.

The invention is particularly suitable for highly loaded metal halide lamps in which the ratio between the inner length and the maximum inner diameter of the discharge vessel, the so-called aspect ratio, is between 1.0 and 8.0, preferably at least 1.5. Limits are included.

Manufacturing technology, it is advantageous that the width of the lamellae is of the order of the wall thickness of the central part of the discharge vessel, and in the case of constant width in particular at most 50%, preferably at most 25%, deviates from this wall thickness.

In particular, the tailpipes are advantageously designed as capillaries. But you can also run differently, see for example DE-A 197 27 429 where a cermet pin is used. The invention is also applicable to plug technologies, wherein the slats either sit on the discharge vessel, or on the separate plug part, or can sit on both bodies slats.

Particularly good cooling effect can be achieved if the lamellae sit on a part of the tailpipes that is adjacent to the ends, or if the lamellae start at the ends.

In general, the lamellae have two broad sides and a narrow side, the narrow side pointing radially outward. These sides together define the surface of the lamella. Particularly preferably, the narrow side can be bevelled and in particular be provided with a coating. The coating should be highly viscous. Suitable materials are especially graphite or carbon, so other carbon modifications such as DLC (diamond-like carbon).

In general, the cooling behavior can also be controlled by covering a part of the tailpipe, in particular a part of the lamella like the narrow side, with a coating of high emissivity. It is also possible to use a coating on the tailpipe without simultaneous use of a lamellar projection at this point.

As the material of the piston A1203, in particular PCA, or any other conventional ceramics such as AlON or AIN can be used. The choice of filling is subject to no particular restriction.

Depending on the filling composition, discharge vessels or burners for high-pressure lamps with approximately uniform wall thickness distribution and slim-running end shapes exhibit, in some cases, high color scattering due to the strong distribution of the metal halide filling in the interior of the discharge vessel. Typically, the charge in the discharge-away region condenses behind the line defined by projection of the electrode tip onto the inner burner surface. The filling position on a zone of the surface in the interior of the discharge vessel, which corresponds to a narrow temperature range, and in the residual volumes of -eventuell-existing capillaries into is not sufficiently accurately adjustable. Therefore, it is now important to apply fins or lamellae to the discharge vessel, the effect of which predominantly occurs in an area which lies behind the line which is determined by projecting the electrode tip onto the inner burner surface. In particular, predominantly means that at least two-thirds of the surface of the fins is mounted in an area which is behind the line away from discharge, which is determined by projection of the electrode tip on the wall of the discharge vessel.

Previous discharge vessels often have a shape with increased wall thickness at the end surfaces, eg in cylindrical burner shapes, thereby creating an enlarged end surface. Another problem is the increased by the wall thickness-dependent specific emission coefficient of the ceramic radiation of IR radiation during operation of the discharge vessel in the evacuated or gas-filled outer envelope. In this case, the surface of the discharge vessel determined by the specific radiation power according to the Stefan Boltzmann law: $${\mathrm{P}}_{\mathrm{wheel}}\mathrm{/}\mathrm{A}\mathrm{=}\mathrm{\epsilon }\mathrm{*}\mathrm{\sigma }\mathrm{*}{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">T</figure-callout>}}^{\mathrm{4}}\mathrm{,}$$

It is
P _rad / A: radiated radiant power per unit surface area;
ε = hemispherical emission coefficient of the radiating surface,
σ = Stefan Boltzmann constant,
T = surface temperature.

In this way, a concentrated charge distribution is generated by a heat sink effect at the end of the discharge vessel, which determines the vapor pressures of the metal halides used in the discharge vessel such that a sufficient for ceramic lamp systems color scattering value of typically ≤ 75 K for larger lamp groups the same operating performance is adjustable.

In spherical discharge vessels, or those with Halbkugelendformen or tapered end shapes or elliptical shaped end shapes and cylindrical center portion relatively high aspect ratios IL / ID of about 1.5 to 8, particularly serious problems arise. Due to the slim transition into the region of the tailpipe, usually a capillary area, partially insufficient cooling effects at the end of the discharge vessel and thus an insufficient determination of the temperature, which is not sufficient for a concentrated charge deposit in a narrow temperature range of the inner wall.

According to the invention, essentially two mechanisms for intensified cooling of the end of the discharge vessel are provided. Thus, the transition of the discharge vessel in which the arc discharge burns is meant to the end forms containing the electrode structures for electrical or electromagnetic line coupling. This applies in particular, if no significant increase in the wall thickness in the end region relative to the wall thickness of the discharge vessel - in cylindrical discharge vessels are typically around a factor of 1.5 to 2.5-- is given by the shaping. However, an application for this is not excluded.

Essential is the enlargement of the surface by integrally formed in the transition region to the tail pipe wing-like or fin-like formations, preferably with longitudinal alignment parallel to the axis with at least threefold symmetry and a maximum achtzähliger symmetry of the distribution around the circumference. In particular, they are slats.

The fin-like molding areas may be substantially smooth surfaces or be formed on the surface faceted. In particular, the facet regions can be delimited over the entire surface area of the lamella and have a defined orientation relative to the axis and to the center of gravity of the discharge vessel.

In addition u.U comes a coating with a material that in the near infrared (NIR), which is typically a wavelength range between 1 and 3 microns, compared to the ceramic material has an increased hemispherical emissivity ε in the temperature range between 650 and 1000 ° C. The coating should preferably be applied in the region of the transition between the end of the discharge vessel and tailpipe. In particular, this also applies to the tailpipe alone, where the coating can be applied without a lamella.

High-temperature-resistant coatings with hemispherical emission coefficients ε, preferably ε ≥ 0.6, are suitable as coating materials. Among them is graphite, mixtures of Al2O3 with graphite, mixtures of Al2O3 with carbides of the metals Ti, Ta, Hf, Zr, as well as of semi-metals such as Si. Also suitable are mixtures which additionally contain other metals for adjusting any desired electrical conductivity.

Of course, both measures can be suitably combined with each other, so that part of the surface radiation increase takes place via an enlargement of the surface by fins and at the same time a part by the coating of parts of these fins or the adjacent colder tailpipe areas.

1. 1. Effektivere Kühlung bei gleichzeitig relativ geringer zusätzlicher Keramikmasse;
2. 2. Verringerung des longitudinalen Wärmeflusses in die Endrohr;
3. 3. deutlich vergrößerte Flexibilität der Oberflächeneinstellung im Endenbereich;
4. 4. Verringerung der Abschattungseffekte im Raumwinkelbereich der Elektrodenzuführung;
5. 5. Einstellbarkeit effektiver lokaler Thermostatwirkung mittels relativ kleiner Oberflächenbereiche.

Overall, there are a number of advantages when using integral lamellae in ceramic discharge vessels:

1. 1. More effective cooling with relatively low additional ceramic mass;
2. 2. Reduction of the longitudinal heat flow into the tailpipe;
3. 3. significantly increased flexibility of the surface adjustment in the end region;
4. 4. reduction of shading effects in the solid angle range of the electrode feed;
5. 5. Adjustability of effective local thermostatic effect by means of relatively small surface areas.

These properties are particularly important for highly loaded forms of discharge vessels with a small total surface area and possibly increased aspect ratio, since under these conditions a local cooling by heat flow over relatively large wall cross-sectional areas becomes difficult.

The total mass of the discharge vessel increases only insignificantly by this type of fins and thus remains below a critical value that would adversely affect the start-up behavior of the lamp when ignited. There is thus a sophisticated compromise between good ignition and effective cooling. This measure allows a very high color stability under the conscious acceptance of a bad isotherm. This is done in departure from the previous objective of the best possible isotherm and allows the zone of condensation of the filling to be determined exactly by deliberately designing a temperature gradient.

In the complete absence of a coating, the area of the lamellae is optically transparent or at least translucent. If possible, this should also be the goal for areas with coating. To approximate this goal, the solid angle below which the areas of coating appear from the center of the lamp is minimized as much as possible. Because the coating absorbs radiation and therefore costs efficiency. For this reason, the coating should be applied to inclined surfaces of the slats, since then from the center of their solid angle smaller appears. This applies in particular to the narrow side of the slats. An alternative is to place the coating as far back as possible on the lamella and / or the tailpipe, since this also reduces the effectively shaded solid angle. In this way, an optimal value of the cooling can be achieved while maintaining optimum efficiency. Particularly effective coatings are graphite and TiC.

A control means of the cooling effect is also the maximum height of the blade, especially if it attaches to the discharge vessel, since depending on the approach height, the discharge takes place from a different temperature level.

A particular advantage of such integral lamellae is that they are particularly effective at cooling compared to separate lids, and that they are easy to manufacture using modern manufacturing techniques such as injection molding, slip casting or rapid prototyping.

Brief description of the drawings

Fig. 1

eine Hochdruckentladungslampe;

Fig. 2

ein detail der Entladungslampe aus Figur 1;

Fig. 3, 5a, 5b, 10

Ausführungsbeispiele eines Entladungsgefäßes;

Fig. 4, 6-9

weitere Entladungsgefäße;

Figur 11

eine schematische Darstellung der geometrischen Parameter der Lamellen;

In the following, the invention will be explained in more detail with reference to several embodiments. The figures show:

Fig. 1

a high pressure discharge lamp;

Fig. 2

a detail of the discharge lamp FIG. 1 ;

Fig. 3, 5a, 5b, 10th

Embodiments of a discharge vessel;

Fig. 4, 6-9

further discharge vessels;

FIG. 11

a schematic representation of the geometric parameters of the slats;

Preferred embodiment of the invention

FIG. 1 It consists of a tubular discharge vessel 2 made of ceramic, in which two electrodes are inserted (not visible). The discharge vessel has a central part 5 and two ends 4 at the ends sit two tailpipes 6, which are designed here as capillaries. Preferably, the discharge vessel and the tailpipes are integrally made of a material such as PCA.

The discharge vessel 2 is surrounded by an outer bulb 7, which terminates a base 8. The discharge vessel 2 is supported in the outer bulb by means of a rack including a short and long power supply 11a and 11b. At the tail pipes 6 are each slats 10 which extend like a fins radially outward.

FIG. 2 shows a plan view of the region of a tailpipe 6. the fins 10 have two broad sides 12 and a narrow side 13. The fins are vierzählig evenly distributed around the tailpipe. On the narrow sides 13, which are bevelled, sits a highly explosive layer 14 of graphite or carbon. The fins have a maximum height of about half the maximum height of the central part of the discharge vessel.

FIG. 3 shows a discharge vessel 2, wherein in the left-hand embodiment, the fins 15 branch off from approximately the maximum height of the end of the discharge vessel and maintain the height. In the right-hand embodiment, the mass of the blade is significantly lower by the maximum height of the blade with increasing distance from the end 4 decreases evenly. These two embodiments illustrate that the shape of the slat can be matched exactly to the current needs. The number, total mass and length of the slats can be optimized according to the desired degree of cooling.

FIG. 4 shows on the left possibility to effect the cooling only by a coating 16 which completely surrounds the tailpipe 6 like a cuff in its middle part. On the right, a type of lamella 17 is shown, which is located only on the tailpipe 6 itself and does not extend further to the discharge vessel 2, which is here separate from the capillary. The lamella 17 is here shaped like a circle segment.

FIG. 5 shows in the left embodiment, a discharge vessel 19 with a short tailpipe 20 and very short fins 21, but a total of eight fins are used. FIG. 5 further shows in the right embodiment of an arrangement in which these slats additionally a rotationally symmetric. Coating 22 is used after the fins.

Further embodiments are those with a higher numbering than 8, in particular up to 16. The number of fins does not have to be even, it can also be odd, for example five fins. Another embodiment is characterized in that differently designed groups of lamellae are used, for example two groups on a tailpipe whose width and height are different and which alternate.

Each fin or fin has a given maximum height that extends radially to the axis of the discharge vessel and a maximum length that extends axially and a maximum width. All three sizes can have a constant value, but they usually vary so that they are optimally adapted to the needs.

The length L of the fin or lamella can range from a fraction of the total length GL of the discharge vessel including the length of the tailpipes themselves, in particular of at least one twentieth, to half the total length. So 1/20 GL ≤ L ≤ 0.5 GL. In the case where L = 0.5 GL, then the fin and its counterpart at the other end together effectively extend over the entire discharge vessel.

The height H of the fin or lamella may vary from a fraction, in particular one tenth, of the difference DF between half the maximum outer diameter of the discharge vessel and the half diameter of the capillary up to twice, in particular 1.4 times, particularly preferably to the simple, this difference DF range. So 1/10 DF ≤ H ≤ 2 DF. Preferably, 1/5 DF ≦ H ≦ 1.4 DF. The fins may also be stepped, that is, their height H varies in steps along the length L.

The width B of the fin is often constant and usually ranges from 0.2 to 1.5 mm. A second preferred embodiment is a radially outwardly decreasing width. Also possible is an outwardly increasing width, wherein in particular the arc length BL of the width B remains constant. A typical arc length BL is 1/10 of the circumference U of the tailpipe down to 1/50 U. Thus, 1/50 ≦ BL / U ≦ 1/10. Another shape of the width of the fin is triangular or in particular trapezoidal, seen in cross section.

The longer the fins, the lower the wall thickness of the discharge vessel or the capillary can be selected. If the fins are pulled over the entire axial length of the tailpipe, usually a capillary, this greatly increases the surface area of the tailpipe. Comparing an unstructured tube as the tailpipe with a finned tube of the same outside diameter, the heat flow to the ends is reduced by the reduced cross-section.

FIG. 6 shows a discharge vessel 25 with lamellae 26, in which the height H changes continuously from the value zero inwards to a maximum of approximately H = 0.5 DF.

FIG. 7 shows a discharge vessel 25 with stepped blades 27, so that the height H of the blade changes abruptly. In addition, the definition of the total length GL is shown here.

FIG. 8 shows a cylindrical discharge vessel 30 with stepped blades 26, in which the fins extend over the entire length of the tail pipe. A lower part 26a of the blades is pulled to the end of the discharge vessel, the height of the blades continues to increase in two stages. Part 26b has about 50% of the height corresponding to the diameter of the discharge vessel and part 26c has 100% of the height of the diameter of the discharge vessel.

FIG. 9 shows a cylindrical discharge vessel 30, in which the entire length of the discharge vessel is coated with fins 35.

FIG. 10 shows a representation of the end 36 of a discharge vessel, which is closed by a separate plug 37. The blade 38 here has the shape of a fin, which attaches just behind the line PL and then extends approximately to the approach of the tail pipe 39. Small fins 40 are additionally arranged on the plug 37.

At the same time, the term projection line PL at the tip of the electrode 41 is explained in this figure. The essence of the invention resides in that at least at one end of the discharge vessel there are fin-like fins, as shown here as 38, which extend radially outwards in their height H, the surface of the fins is arranged predominantly in a region which is located away from discharge behind a line which is determined by the projection of the tip of the electrode on the inner surface of the discharge vessel. Preferably, this proportion is at least two-thirds. But it can be up to 100%. The fin can only extend between the projection line PL and the projection AA of the tailpipe, where it exerts the highest effect, or extends further back to a part or the entire length of the tailpipe. But it can also be located only in the tailpipe. The dashed lines show possible embodiments of the fin.

FIG. 11 shows a scheme for explaining the concepts of height H, width B and length L of the slats. In the case of variable size of the dimensions H, B and L, in each case a maximum height, width or length is meant.

Claims (10)

1. High-pressure discharge lamp (1) having a ceramic discharge vessel (2) with a central part (5) and two ends (4), on which two end tubes (6; 39) are positioned, electrodes being anchored in the end tubes and extending into the discharge volume enveloped by the discharge vessel, a filling, which contains metals and/or metal halides, being accommodated in the discharge volume, fin-like laminates (15) being positioned at least on one end (4) and extending radially outwards at their height H, the surface of the laminates being arranged in a region which is positioned, remote from the discharge, behind a plane which runs through the tip of the electrode and perpendicularly to a longitudinal axis of the lamp, and characterized in that the laminates (15) and the discharge vessel (2) are produced integrally from Al₂O₃, AlON or AlN.
2. High-pressure discharge lamp according to Claim 1, characterized in that the arrangement of the laminates (15) is such that they are rotationally symmetrical to one another, in particular with a three-fold to eight-fold symmetry.
3. High-pressure discharge lamp according to Claim 2, characterized in that the form of the laminates (15) is substantially identical or is identical in groups.
4. High-pressure discharge lamp according to Claim 1, characterized in that the wall thickness of the laminates (15) approximately corresponds to the wall thickness of the central part (5) of the discharge vessel, to be precise in particular deviates from this by at most 50%.
5. High-pressure discharge lamp according to Claim 1, characterized in that the end tubes are in the form of capillaries (6).
6. High-pressure discharge lamp according to Claim 1, characterized in that the laminates have two broad sides and one narrow side, the narrow side being positioned radially on the outside.
7. High-pressure discharge lamp according to Claim 6, characterized in that the narrow side is beveled and in particular is provided with a coating.
8. High-pressure discharge lamp according to Claim 1, characterized in that part of the end tube, in particular part of the laminate, is covered with a coating having a high emissivity.
9. High-pressure discharge lamp according to Claim 6, characterized in that at least one laminate has subareas of different heights H which are delimited by at least one edge, and at least one of these subareas is provided with a coating.
10. High-pressure discharge lamp according to Claim 1, characterized in that the discharge vessel has a bulging shape, with the result that the diameter of the discharge vessel reduces in size towards the ends.

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