Patent Publication Number: US-6707238-B2

Title: Compact low-pressure discharge lamp

Description:
TECHNICAL FIELD 
     The invention relates to a compact low-pressure discharge lamp comprising a discharge vessel with electrodes and power supply leads, a discharge vessel mount on which the discharge vessel is mounted, and a cap, which comprises a housing, connecting contacts and a mounting plate with a ballast apparatus, with the mounting plate being fitted with the ballast arrangement in the interior of the cap housing, and having connections for electrical connection of the mounting plate to the power supply leads and to the connecting contacts. 
     BACKGROUND ART 
     Compact low-pressure discharge lamps such as these may also be provided with a reflector or an enveloping bulb. For relatively high wattages, the discharge vessel in this case comprises a tube which is composed of one or more pieces and is bent a number of times, and which is held in the housing with the aid of a mount part, whose shape is complex and which is composed of plastic or metal. One example of this is described in U.S. Pat. No. 4,456,854. 
     The mount part, whose shape is complex, for the discharge vessel leads firstly to correspondingly large dimensions for the low-pressure discharge lamp and secondly necessitates manual assembly of the lamp. The production costs for such compact low-pressure discharge lamps are thus relatively high. 
     DISCLOSURE OF THE INVENTION 
     The object of the invention is to provide a compact low-pressure discharge lamp of the type mentioned initially, which has a compact structure and can be produced easily, and hence cost-effectively. 
     In the case of the compact low-pressure discharge lamp according to the invention, the object is achieved by a mount for the discharge vessel having an essentially H-shaped cross section, with the mount comprising a plate with collars which run on the edge of each side of the plate. A cover part on the one hand and the housing of the cap on the other hand are now mounted on this discharge vessel mount. 
     The cover part may be in the form of an enveloping bulb or a reflector for the discharge vessel. If the compact discharge lamp is to be configured without an enveloping bulb or reflector, this cover part may also be in the form of a closure cap for the cap housing. 
     In the case of a circular-cylindrical cap housing, the plate of the H-shaped discharge vessel mount is advantageously circular. 
     The mounting of the discharge vessel is simple if the plate of the discharge vessel mount has two apertures or depressions in the form of half shells for holding the ends of the discharge vessel. The ends can then be mounted on the plate either by means of a hot fusion method, as is described in WO 0,101,437, or in a conventional manner by means of cap cement or adhesive. In the second case, the plate advantageously has a holding edge, for holding the cap cement or adhesive, around the apertures or depressions in the form of half shells, in which case, where apertures are used, the holding edge is advantageously fitted on the side of the plate facing the cap and, where depressions in the form of half shells are used, it is fitted on the side of the plate facing the cover part. 
     The discharge vessel can also be mounted on the discharge vessel mount by means of a trough, into which a part of the discharge vessel, such as a bend, is inserted. This type of mounting may also additionally be worthwhile for fixing the two ends of the discharge vessel, especially when the discharge vessel is long and has a number of bends. 
     On the side facing the cap, the plate also preferably has holders for contacts for electrical connection of the power supply leads to the electrical connections of the ballast arrangement on the mounting plate. One example of corresponding contact-making is contained in U.S. Pat. No. 6,008,570, where a cost-effective electrical connection between the power supply leads of the discharge vessel and the connections of the ballast arrangement on the mounting plate is produced by means of spring elements, which are held in holders on the closure cap. 
     In order to hold the cover part in a simple manner on the H-shaped discharge vessel mount, the latter has an at least partially circumferential groove on the inner face of its casing surface, in which groove formed-out regions, in the form of hooks, of the collar (facing the cover part) on the plate engage. 
     In order to mount the cap on the H-shaped mount, the cap housing has an at least partially circumferential groove on the inner face of its casing surface, in which groove formed-out regions, likewise in the form of hooks, on the other collar (facing the cap housing) of the plate engage. 
     Each collar advantageously has between 2 and 8 formed-out regions in the form of hooks. The formed-out regions in the form of hooks in this case have a width of between 1 and 30 mm depending on the cap housing diameter and—with respect to the two collars—are arranged laterally offset with respect to one another, so that the projections of the formed-out regions, in the form of hooks, do not overlap in a plane at right angles to the lamp axis. 
     One or more relatively broad slots are incorporated in the collars facing the cover part and/or the cap housing, into which slots corresponding mating pieces in the form of ribs on the cover part and/or cap housing engage, thus producing protection against twisting. This avoids forces acting on the formed-out regions, in the form of hooks, when torques act about the lamp axis, so that the formed-out regions need absorb only tensile forces. This avoids the formed-out regions, in the form of hooks, breaking off, and avoids the connection becoming undone. 
     The formed-out regions in the form of hooks on the two collars are furthermore subdivided into a number of segments by narrow slots which extend as far as the plate. This segmentation leads to a reduction in the joining force. The number and width of the these segments are matched to one another such that, making use of the protection against twisting described above, the strength values required in the relevant Standards are complied with, and the joining forces are in a range which can also easily be coped with for manual assembly. 
     In addition, apertures can be provided on the plate, for holding tools to engage in. This allows fully automated assembly of the mount plate, fitted with the discharge vessel, together with the cover part, which is in the form of an enveloping bulb, reflector or closure cap, and the cap. 
     The H-shaped mount is composed of plastic, with the material advantageously being transparent. 
     The cover part is preferably composed of plastic, in which case, if the cover part is in the form of an enveloping bulb, it may comprise a glass bulb with a plastic edge fitted to it. 
     The optional configuration of the cover part as an enveloping bulb, reflector or closure cap makes it easy in production to change from compact low-pressure discharge lamps without enveloping bulbs to the same lamp type with an enveloping bulb or reflector. The pure plug-in and latching connections allow the lamp to be assembled very much more easily and fully automatically. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details, features, refinements and advantages can be found in the following description of a number of exemplary embodiments, which are illustrated in drawings, of the subject matter of the invention, in which: 
     FIG. 1 shows a sectioned side view, illustrated partially schematically, of the low-pressure discharge lamp according to the invention with an enveloping bulb; 
     FIG. 2 shows a sectioned side view, illustrated partially schematically, of the low-pressure discharge lamp according to the invention with a reflector; 
     FIG. 3 shows a sectioned side view, illustrated partially schematically, of the low-pressure discharge lamp according to the invention with a closure cap. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 1 shows a sectioned side view of a compact low-pressure discharge lamp  1  according to the invention with a cover part which is in the form of an enveloping bulb  2  and is composed of plastic. The lamp has a discharge vessel  3  which is wound a number of times and has an amalgam filling. The ends of the discharge vessel are pushed into apertures in the circular plate  4  of an H-shaped discharge vessel mount  5  composed of plastic, and are mounted by means of cap cement (which cannot be seen here) in the holding edge  6  (which is in the form of a bead) around the apertures. The electrodes, which are fused into the ends of the discharge vessel  3 , are connected via power supply leads  7  to contacts, which are mounted by means of holders  8  on the H-shaped discharge vessel mount  5 . 
     The H-shaped discharge vessel mount  5  has, on the edge of its plate  4 , a collar  9  which extends in the direction of the enveloping bulb  2  and has formed-out regions  10  which are in the form of hooks and engage in an at least partially circumferential groove  11  on the inner wall of the enveloping bulb  2 . This creates a connection which cannot be detached by those not skilled in the art between the H-shaped discharge vessel mount  5  and the enveloping bulb  2 . Protection against twisting between the enveloping bulb  2  and the discharge vessel mount  5  is achieved by four formed-out regions  10 , in the form of hooks, on the collar  9 , which engage in corresponding groove sections  11  in the region of the neck of the enveloping bulb  2 . As a result of this, when torques are applied, no forces are produced on the formed-out regions which are in the form of hooks and secure the mechanical connection, hence protecting them against damage. The grooves and the formed-out regions in the form of hooks are arranged with 90° symmetry. This ensures that, when the enveloping bulb  2  is fitted, both parts are in the joining position at the latest after being rotated through 90°, and are then connected to one another by application of the joining force. This is advantageous during assembling. 
     The low-pressure discharge lamp  1  also has an essentially cylindrical cap  12  with a housing  13  and schematically illustrated connecting contacts  14 . A mounting plate  15 , which is in the form of a circuit board, is located at right angles to the lamp longitudinal axis in the interior of the housing  13 . Conductor tracks are formed on the side of the circuit board facing the discharge vessel  3 , and the circuit elements of a ballast arrangement  16  (illustrated schematically) are mounted on the side facing away from the discharge vessel  3 . 
     The housing  13  of the cap  12  is connected to the discharge vessel mount  5  via formed-out regions  17 , which are in the form of hooks and likewise cannot be detached by those not skilled in the art, on the further annular collar  18 , on the side of the plate  4  facing the cap  12 , with the formed-out regions  17  in the form of hooks engaging in an at least partially circumferential annular groove  19  on the inner wall of the casing surface of the housing  13 . Both collars  9 ,  18  have a number of narrow slots  20 , which are distributed over the circumference, parallel to the axis of symmetry of the H-shaped mount  5 , which slots  20  extend as far as the plate  4 , as well as broader slots  21 , in which the corresponding ribs  22  on the inner casing surface on the neck of the enveloping bulb  2  and on the cap housing  13  engage. The narrow slots are used for segmentation of the formed-out regions, in the form of hooks, and for reducing or adjusting the joining force. The broad slots are likewise used in conjunction with the ribs to provide protection against twisting between the cap  12  and the discharge vessel mount  4 , and for correct alignment of the contact elements in the holders  8  with respect to the corresponding contacts on the upper face of the mounting plate  15 . 
     In the embodiment of the discharge vessel mount  5  according to the invention, the formed-out regions in the form of hooks on the collars  9  and  18  are produced such that their projection onto the plane at right angles to the lamp axis has no overlap. This has the advantage that a mould without a slide can be used for injection moulding of the discharge vessel mount  5 . 
     FIG. 2 shows a low-pressure discharge lamp according to the invention, having a reflector  21 . In this case, the cover part is not in the form of an enveloping bulb, but is in the form of a reflector  21 . The other components and the way in which these parts are connected correspond to the low-pressure discharge lamp with an enveloping bulb as illustrated in FIG.  1 . 
     FIG. 3 shows a low-pressure discharge lamp according to the invention having only a closure cap  22 . The cover part is in this case in the form of a closure cap  22 . All the other parts and connections are the same.