GB2062958A

GB2062958A - Sealed beam lamp

Info

Publication number: GB2062958A
Application number: GB8035674A
Authority: GB
Original assignee: Thorn EMI Ltd
Current assignee: Thorn EMI Ltd
Priority date: 1979-11-12
Filing date: 1980-11-06
Publication date: 1981-05-28
Also published as: GB2062958B

Abstract

In a sealed beam lamp unit a tungsten halogen lamp is mounted by rigid leads (15) and preferably a support (17) extending through holes in the wall of the reflector (11). A rigid annular clamping element (23) or eyelet passes through each hole and the lead or support passes through the clamping element and is sealed to it, e.g. by solder 30. To seal the clamping element to the reflector wall the clamping element has around it a sealing element (24) compressed into sealing relationships between the wall and the clamping element by axial pressure from end flanges (26, 28) of the clamping element. The sealing element may be a double flange element or grommet or may, preferably with suitable shaping of the reflector wall, be a single-flanged bush or an "O"-ring. <IMAGE>

Description

SPECIFICATION Sealed beam lamp The present invention relates to sealed beam lamp units, and more especially to lamp units in which a halogen cycle incandescent lamp is sealed in a reflector and refractor assembly, for example for use as a vehicle headlight.

The tungsten halogen lamp requires a bulb wall temperature that limits the size of the bulb for a given input power. With these lamps, therefore, it is no longer possible to design a sealed beam unit in which the reflector and refractor form part of the filament envelope. Instead, headlight have reverted to separate bulb and reflector and refractor units.

The separate structure does, however, retain the disadvantages which led to the earlier development of sealed beam units, namely its liability to take in moisture and dirt with changes in atmospheric pressure and temperature, leading to degradation of the surfaces of the reflector or refractor and progressive diminution in light output.

It is theoretically possible to seal a complete tungsten halogen bulb inside a larger evacuated sealed beam enclosure, but this is not economically acceptable owing to the high cost of the hermetically sealable enclosure, which must be added to the cost of the bulb itself. The provision of a low cost enclosure for the bulk, not capable of sustaining a high vacuum but sealable sufficiently to prevent the ingress of vapour or dust during the normal life of the lamp, raises the problem of mounting and sealing the bulb inside the enclosure while providing for focussing or optical adjustment of the position of the bulb.

One construction of a sealed beam lamp unit of this type and a method of making that lamp are described and claimed in British Patent Applications 2015822A and 2019548A respectively. The lamp unit described has a glass or plastics reflector envelope through which lead-in conductor supports for the tungsten halogen lamp extend. The supports actually extend through and are connected to metal eyelets, themselves extending through holes in the reflector and being fastened to holes in the reflector by adhesive. The position of the bulb inside the envelope can be adjusted prior to said fastening.

However to provide a practical lamp unit which will remain effective during a long active and inactive life it is important that the unit must remain hermetically sealed. It must withstand internal to external gas pressure differentials of the order of half an atmosphere or more while the temperature of parts of it may change by as much as 200"C in less than a minute. Under these conditions the sealant must remain sealed to the envelope and the eyelet. It is also desirable to employ a mounting assembly which is suitable for glass and plastic reflectors and the metal reflectors which are often favoured in the transport industry.

It is an object of the present invention to provide an improved means for mounting and sealing a bulb inside an enclosure which enables the position of the bulb relative to the enclosure to be adjusted and thereafter fixed in the desired position. Although primarily intended for use with tungsten halogen lamps, the invention can, of course, be employed to mount and seal any kind of lamp bulb inside a larger enclosure.

According to the invention there is provided a mounting assembly for holding and sealing in the wall of an enclosure a lamp bulb which is provided with at least one rigid external support or lead wire, the assembly comprises a rigid but deformable annular clamping element having an axial opening forthe passage of the lamp support or lead and being axially compressible to provide a pair of opposed external annular flanges; and a resilient, heat resistant annular sealing element mounted on and encircling the clamping element, such that the assembly can be inserted in an opening in the enclosure wall and the sealing element compressed into sealing relationship between the wall and the clamping element by the said flanges upon axial compression of the clamping element, whereby the lamp support or lead can be held and sealed in the wall.

When such an assembly is employed in securing and sealing a bulb in a lamp enclosure, there is obtained a sealed lamp unit comprising a sealed enclosure the walls of which provide a reflector and a light-transmitting cover or refractor, and a lamp bulb mounted inside the enclosure and having rigid conductive leads and a rigid external support or conductive lead passing through openings in a wall of the enclosure, at least one of the rigid leads or support being held and sealed in the opening by a mounting assembly comprising an annular clamping element surrounding the lead or support and having opposed external annular flanges disposed on opposite sides of the enclosure wall, and an annular sealing element of resilient, heat resistant material disposed around the clamping element and compressed into sealing relationship between the enclosure wall and the clamping element by axial pressure of the said flanges, the lead or support being sealed in substantially gas-tight manner to the clamping element.

The bulb will require two conductive leads, and these may be made substantially rigid and used to support the bulb inside the enclosure, each lead being held and sealed in the enclosure wall by a mounting assembly as defined above. It has, however, been found preferable not to support the bulb by the lead wires alone, because these tend to flex with acceleration forces on the bulb when the lamp unit suffers mechanical vibration or shock, and the lead wires may eventually break or cause chipping and breakage of the vitreous material of the bulb at the points of emergence of the leads. It is therefore preferred to fit an additional rigid support to the bulb, such a support being held and secured in the enclosure wall by a mounting assembly in a similar manner to the leads.The three-point support of the bulb thus provided gives a triangulated system whereby focussing of the lamp unit by accurate positioning of the bulb within the enclosure can be readily achieved.

This focussing facility is of particular importance because of the impracticability of focussing by other techniques. In sealed beam lamps where the outer enclosure constitutes the bulb or envelope it is relatively easy to position the filament accurately in assembly of the lamp. Where a bulb is to be inserted into a reflector/refractor assembly as a separate unit, it can be provided with a cap having reference points with which the filament of the lamp is aligned before the cap is fixed, and the reflector/refractor assembly is provided with corresponding reference points which ensure correct disposition of the bulb. In tungsten-halogen lamps it is difficult to avoid relatively wide tolerances in bulb dimensions and the provision of an accurate predetermined mechanical support is correspondingly expensive. The method of construction shown in the said Application No.

2019548A, using the mounting assembly described in Application No. 2015822A, does provide such a focussing ability. However, it is important to provide such a construction which allows this focussing procedure and further gives adequate sealing for a typical lamp life.

Accordingly, the invention also provides a method of mounting a lamp bulb in the enclosure of a sealed lamp unit, the method including inserting, in an opening in the wall of the enclosure a deformable annular clamping element and a resilient, heat resistant annular sealing element disposed around the clamping element; axially compressing the clamping element and thereby deforming it to press the sealing element into sealing relationship with the wall of the enclosure; inserting a rigid support or lead wire of the bulb through the clamping element; moving the bulb relative to the wall of the enclosure into a desired focussing position; and securing the bulb in the desired position by sealing the support or lead to the clamping element Reflectors and refractors for sealed lamp units can be made of a variety of materials, especially if they are not to be highly evacuated.Metal, plastics and glass can all be used, and the invention has the advantage that it is applicable equally to envelope walls of many different compositions.

The invention will be further described, by way of example, with reference to the accompanying drawings in which like numerals indicate like parts. In the drawings: Figure 1 is a vertical section through a sealed lamp unit embodying the invention; Figure 2 is a fragmentary horizontal section through the lamp of Figure 1; Figure 3 is a front view of the lamp of Figures 1 and2; Figure 4 is a section of one example of a mounting assembly according to the invention, in which the sealing element is of grommet form; Figure 5 is a section of another example of a mounting assembly, in which the sealing element is of flanged bush form; Figure 6shows a modified version of the assembly of Figure 5 fitted to a glass or plastics reflector; and Figure 7 is a further example of an assembly, in which the sealing agent is an O-ring.

In Figures 1 to 3 is shown an example of a sealed beam lamp unit incorporating the invention. An enclosure 10 is constituted buy a concave reflector 11, which may for example be parabolic, and a transparent cover 12 which may be shaped to serve as a refractor, sealed around its periphery to the reflector.

A lamp bulb 13, which may be a tungsten-halogen lamp, including a filament 14, is provided with two substantially rigid external lead wires 15 which extend through respective openings in the reflector 11. A metal box 16 fits over and grips the pinch or press-seal region of the lamp 13 and a rigid support 17 is welded or otherwise fixed to the box and extends through a third opening in the reflector The leads 15 and support 17 are held and sealed in the openings in the reflector 11 by respective mounting assemblies 18 in accordance with this invention and are provided with terminal lugs 19 by means of which electrical connections to the lamp can be made. A fibre disc 20 prevents undesirable rotation of the terminal lugs.

Although a single filament lamp of the type known as H3 is shown in Figures 1 to 3, it will be apparent that the invention is equally applicable to other types of lamp. For example, if a larger, two-filament bulb such as the H4 type is employed, the metal box 16 and support 17 may be connected to one lead of the bulb and used as a supply lead.

One example of a mounting assembly 18 in accordance with the invention, which may be used in the lamp unit of Figures 1 to 3, is shown in greater detail in Figure 4. A support 17 or, as illustrated, a lead 15 is to be held and sealed in an opening in the concave reflector 11, which in the region of the opening is formed with a depression 22 having a flat floor region to receive the mounting assembly. The assembly comprises an annular clamping element 23, in this example in the form of an eyelet, surrounding the lead or support, and a resilient annular sealing element 24 in this example in the form of a grommet, surrounding the eyelet. The edge of the reflector surrounding the opening is received between the flanges of the grommet, which itself lies between the flanges of the eyelet.

The assembly also includes a washer 25 disposed between the inner flange 26 of the eyelet 23 and the grommet 24, a heat-insulating separator or spacer 27 also surrounding the eyelet on the outer side of the grommet, a terminal lug 19 disposed between the separator and the other flange 28 of the eyelet and a closure disc or washer 29 disposed outside the eyelet, and having a hole for the passage of the lead 15. The end of the lead 15 and the outer flange 28 of the eyelet are sealed together in an electrically conductive manner by means of a deposit of solder 30.

In a preferred sequence for fabricating the unit, the grommet 24 is placed in the opening in the reflector 11, and the eyelet 23 in an undeformed condition is threaded through the terminal lug 19, the separator 27 and the grommet. The washer 25 is then placed over the inner end of the eyelet and the latter is opened out to form a flange, the eyelet being compressed axially until the grommet 24 is forced into intimate sealing contact with the wall of the reflector 11 and the barrel of the eyelet 23.

This process is repeated at each of the three openings, whereafter the lamp bulb 13 is introduced and the leads 15 and support 19 threaded through the eyelets in the corresponding openings. The lead and support wires are then gripped and used to adjust the position of the bulb and so to focus the lamp unit. When the lamp is focussed, the wires are soldered to the eyelet and the excess wire cut away.

The disc or washer 29, placed over the wire outside the eyelet, has been useful in preventing excess solder from running down the wire into the eyelet.

The arrangement shown in Figure 4 is particularly suitable for use with a metal reflector, since the grommet 24 provides complete electrical insulation between the lead 15 or eyelet 23 and the wall of the reflector 11. Any suitable metal may be used for the reflector, although stainless steel is preferred.

The sealing element or grommet 24 should be made of a material which is sufficiently deformable to provide a gas- and liquid- tight seal but is stiff enough to restrict elastic deformation in handling or use of the assembled lamp or must closely match the expansion coefficients of the reflector and the eyelet where these are the same. The material must also withstand the heat momentarily conducted through the eyelet at the time of soldering. Although experience would suggest that compressed rubber or plastic materials would not satisfy all of these requirements, it has been found that they can do so.

Suitable materials include rubber compositions as used in the manufacture of motor vehicle tyres, which have been found to have the desired stiffness and heat-resistance, for example Butyl rubber, and the synthetic rubbers "Neoprene" and "Viton" (Registered Trade Mark). The type and percentage of any "loading" of the basic rubber material, that is by carbon black in the case of tyre materials controls the stiffness and resistivity to heat and this should be adjusted for example according to known practices for motor vehicle tyres.

The clamping element or eyelet 23 can be made from almost any ductile metal. Stainless steel and nickel-iron alloys have desirably low heat conductivities but are relatively costly and are difficult to solder consistently in mass production. Copper and its alloys are both costly and good conductors. Aluminium and its alloys are good conductors and difficult to solder. The preferred metal is mild steel, plated with copper or tin for ease of soldering. The same materials can be used for the washer 29.

The melting point of the solder also determines the amount of heat reaching the sealing element or grommet. The preferred solder is 60% tin/40% lead, having a melting temperature of 188 C. Cheaper solders with higher lead contents, such as 20% tin/80% lead, can be used provided the sealing element is resistant to the resulting higher temperature or spaced sufficiently by the use of a long eyelet.

The terminal lugs 19 may be shaped for use with conventional push-on shockets, and are suitably of brass, which may be plated for increased corrosion resistance. Flexible wire connections can replace the terminal lugs if required. The lugs and lead wires assist in conducting heat away from the seal region during operation of the lamp, and seals can remain undamaged with lamp powers as high as 75w in the sealed units.

Although Figures 1 to 3 show a mounting assembly as described in relation to Figure 4, the lamp unit shown in that figure may be used with other forms of mounting assembly in accordance with this invention.

Figure 5 shows an alternative form of mounting assembly, preferred for use with metal reflectors, in which the depression 22 in the reflector 11 is shaped to follow closely the site of the individual mounting, thereby helping to locate the sealing element 24 and washer 25 during assembly and restricting the extent to which the material of the sealing element is squeezed out from under the washer during compression of the clamping element. In such as case, it is not necessary for the sealing element to be in the form of a grommet, and a resilient flanged bush 24a of the same type of material has been found to be satisfactory. The absence of the second flange enables the sealing element to be simply placed in the opening during assembly.This arrangement has been found to be satisfactory particularly where the tubular portion of the bush is as long as the thickness of the reflector and is a close fit between the reflector wall and the eyelet 23.

The spacer 27 performs several functions. It serves to complete the electrical insulation between the terminal lug 19 and the reflector 11, necessary when the reflector is made of metal. It also helps to insulate the sealing element 24 or 24a from the heat of soldering. A washer or collar of thermosetting resin is suitable for this purpose. The collar may be cut to length from tubular plastics stock. It may also be formed of the same material as is used for plastics reflectors, notably with a phenolic or epoxy base. The spacer can also help to prevent rotation of the terminal lug 19 during handling of the unit.

Rotation can be further resisted by applying a fine grit coating to the end faces of the spacer or by the use of adhesive. The tool-marked surface of a spacer cut from tubular stock is also effective in this respect.

Figure 6 shows one form of mounting assembly 18 especially suitable for use with a plastics or glass reflector 1 la. Thickness variations are easily built into a reflector moulded from these materials, and the reflector is preferably formed with a moulded depression 22a having an opening with thickened edges to assist in formation of the seal. Thus in Figure 6, the edge of the opening is stepped to provide an internal flange 32 which directly contacts the eyelet 23 and serves as an insulating spacer. A separator element corresponding to the spacer 27 in Figures 4 and 5 is therefore not required. The close proximity of the side walls of the depression 22a to the sealing element enables the latter to be provided by a flanged bush 24a as in the Figure 5 assembly.

The rear face of the depression is formed with a slot to accommodate and prevent rotation ofthetermi- nal lug 19.

An alternative form of assembly intended for use with a plastics or glass reflector is shown in Figure 7, where the edge of the reflector opening is formed with an angled face 34, for example at about 45 , and the sealing element employed is in the form of an O-ring 24b. This arrangement, in which the washer 26 can be compressed into direct contact with the reflector, provides a structure of enhanced rigidity, but care must be taken to avoid damaging the reflector by excessive pressure. For this reason a washer formed of a more ductile material, for example aluminium, is preferred in this construction.

The invention can be used with conventional plastics and glass reflector materials, for example phenolic or epoxy resins with a substantial content of heat conductive filler or, in the case of glass, hard borosilicate glasses with linear thermal expansion coefficients less than 4.0 x 10-6 per "C.

Claims

1. A mounting assembly for holding and sealing in the wall of an enclosure a lamp bulb which is provided with at least one rigid external support or lead wire, the assembly comprising a rigid but deformable annular clamping element having an axial opening for the passage of the lamp support or lead and being axially compressible to provide a pair of opposed external annular flanges; and a resilient, heat resistant annular sealing element mounted on and encircling the clamping element, such that the assembly can be inserted in an opening in the enclosure wall and the sealing element compressed into sealing relationship between the wall and the clamping element by the said flanges upon axial compression of the clamping element, whereby the lamp support or lead can be held and sealed in the wall.

2. A mounting assembly according to claim 1 in which the annular sealing element is a double flanged grommet.

3. A mounting assembly according to claim 1 in which the annular sealing element is a single flanged bush.

4. A mounting assembly according to claim 3 in which the tubular portion of the bush is of a length substantially equal to the thickness of the envelope.

5. A mounting assembly according to claim 1 in which the annular sealing element is an '0' ring.

6. A mounting assembly according to any of claims 3 to 5 in which the enclosure wall is shaped in the region of said opening at least partly to locate said sealing element.

7. A mounting assembly according to claim 6 as dependent on claim 5 in which the opening in the enclosure wall is provided with a face angled to the axis thereof.

8. A mounting assembly according to any preceding claim in which the annular sealing element is made of motor vehicle tyre material.

9. A mounting assembly according to claim 8 in which the material is butyl rubber.

10. A mounting assembly according to any of claims 1-7 in which the annular sealing element is made of "Viton" (Registered Trade Mark).

11. A mounting assembly according to any of claims 1-7 in which the annular sealing element is made of "Neoprene".

12. A mounting assembly according to any preceding claim in which the clamping element is made of mild steel.

13. A mounting assembly according to claim 12 in which the clamping element is plated with copper ortin.

14. A mounting assembly according to any preceding claim in which the clamping element is an eyelet.

15. A sealed lamp unit including a sealed enclosure, the walls of which provide a reflector and a light-transmitting cover or refractor, and a lamp bulb provided with rigid conductive leads and a rigid external support or lead, the lamp bulb being held and sealed in a wall of the enclosure by means of at least one mounting assembly according to any preceding claim.

16. A mounting assembly substantially as herein described with reference to Figures 1-3 and any one of Figures 4 to 7 of the accompanying drawings.

17. A sealed lamp unit comprising a sealed enclosure the walls of which provide a reflector and a light-transmitting cover or refractor, and a lamp bulb mounted inside the enclosure and having rigid conductive leads and a rigid external support or conductive lead passing through openings in a wall of the enclosure, at least one of the rigid leads or support being held and sealed in the opening by a mounting assembly comprising an annular clamping element surrounding the lead or support and having opposed external annular flanges disposed on opposite sides of the enclosure wall, and an annular sealing element of resilient, heat resistant material disposed around the clamping element and compressed into sealing relationship between the enclosure wall and the clamping element by axial pressure of the said flanges, the lead or support being sealed in substantially gas-tight manner to the clamping element.

18. Asealed lamp unit comprising a sealed enclosure, the walls of which provide a reflector and a light transmitting cover or refractor; a tungsten halogen lamp disposed within the envelope; a metal eyelet passing through a hole in an envelope wall; an annular sealing element of resilient, heat resistant material disposed around the eyelet and compressed into sealing relationship between the enclosure wall and the eyelet by axial pressure of external annularflanges of the eyelet; and a rigid conductive lead our a support which is connected to and supports, at least in part, the tungsten halogen lamp and which passes through and is sealed in substantially gas tight manner to the eyelet.

19. Asealed lamp unit substantially as herein described with reference to Figures 1 to 3 and any one of Figures 4 to 7 of the accompanying drawings.

20. A method of mounting a light bulb in the enclosure of a sealed lamp unit, the method including: inserting, in an opening in the wall of the enclosure a deformable annular clamping element and a resilient, heat resistant annular sealing element disposed around the clamping element; axially compressing the clamping element and thereby deforming it to press the sealing element into sealing relationship with the wall of the enclosure; inserting a rigid support or lead wire of the bulb through the clamping element; moving the bulb relative to the wall of the enclosure into a desired focussing position; and securing the bulb in the desired position by sealing the support or lead to the clamping element.

21. A method according to claim 20 in which the annular sealing element used is a double flanged grommet.

22. A method according to claim 20 in which the annular sealing element used is a single flanged bush.

23. A method according to claim 20 in which the annular sealing element is an "0" ring.

24. A method according to either claim 22 or claim 23 including forming the wall of the enclosure in the region of the opening with a shape suitable to locate said sealing element at least in part.

25. A method according to any of claims 20-24 in which the clamping element used is an eyelet.

26. A method of mounting a lamp bulb in the enclosure of a sealed lamp unit, the method being substantially as herein described with reference to Figure 1 to 3 and any one of Figures 4-7 of the accompanying drawings.