FR2717982A1 - Fluorescent lamp with electromagnetic shielding for car brake light - Google Patents

Abstract

The lamp includes a fluorescent tube (1) enclosed in a box (2) provided with a transparent lid (3). A reflector (4) placed at the back of the box reflects the light towards the lid. The lamp is supplied via a ballast (5) which is connected to the car battery with two cables (7,8). The ballast is enclosed in a conducting cavity (6) which blocks the electromagnetic waves generated by the ballast. The lamp box is made of plastic with graphite particles included in its composition. The box lid presents a metallic mesh (9) made of aluminium or copper.

Description

 The present invention relates to a shielding device against electromagnetic disturbances of lighting and / or vehicle signaling systems comprising a light source of the elongated tubular discharge lamp type such as for example a neon tube or a fluorescent tube.

 In vehicle interior lighting devices, as in vehicle signaling devices, currently used mainly non-radiating electromagnetic waves such as incandescent lamps or diodes.

 However, we have recently seen devices using fluorescent tubes for lighting dashboards for example. But these, although having a large dimension, have a low emission energy and therefore emit very little electromagnetic interference capable of disturbing internal elements of the vehicle.

 However, there are many other applications of lighting and / or signaling systems in which neon or fluorescent tubes are or could be advantageously used. Patent application WO-A93 / 02892 discloses for example a lighting device based on a neon tube for a raised brake light. One can also imagine using devices based on fluorescent tubes for lighting the passenger compartment, in a ceiling lamp for example.

 Now it turns out that these sources, supplied by switching power supplies, emit electromagnetic waves due to the high frequency content of the current which supplies them. Due to the radiation of these electromagnetic waves, interference occurs with other electronic equipment in the vehicle which can seriously disturb its operation. Interference can therefore affect reception of the radio or radiotelephone, but it can also disturb the functioning of an on-board computer or safety equipment, such as an anti-lock braking system, which is much more serious. On the other hand, if the lighting and / or signaling device is located at the rear of the vehicle, disturbances may even occur on vehicles external to it, such as the vehicle following it directly.

 For all these reasons, it is therefore necessary to shield the lighting and / or signaling device using discharge tubes to prevent electromagnetic radiation from leaving it.

 In the case of discharge bulbs fitted to certain headlights of motor vehicles, it is known to create a shielding of the power supply and of the wiring, which are the main sources of emission of electromagnetic waves, by enclosing the power supply and the wiring in a cavity whose wall, electrically conductive, is earthed on the vehicle body. Such a device is disclosed by patent FR-A-2,668,245.

 In the case of neon or fluorescent tubes, because of the large size of the light source, which can range from 15 to 120 centimeters, it is the light source itself which is the main emitter of electromagnetic radiation. However, in the current state of the art, we do not know how to shield this light source because the transparent part of the device allowing the exit of the light cannot be enclosed in a cavity like that described in the previous paragraph.

 In order to remedy these drawbacks, the present invention provides a lighting and / or signaling device for a motor vehicle, comprising a light source of the elongated tubular discharge lamp type, for example a neon tube or a fluorescent tube, the l the envelope is at least partially transparent; a housing enclosing said light source; a supply of said light source; and a transparent cover, allowing the light to exit, characterized in that any one of the transparent envelope or cover elements comprises at least one electrically conductive element, and a means of contacting this conductive element and respectively, an electrically cavity conductive enclosing the power supply of the source or the electrically conductive wall of said housing.

 According to one aspect of the invention, said conductive element comprises a metal mesh overmolded in the material making up said transparent cover.

 According to another aspect of the invention, said means for bringing the electrically conductive element of the transparent cover into contact with the housing of the device comprises a metal mesh, a part of which protrudes from the material making up said transparent cover on at least one edge of that -ci, said parts being able to be folded to form spring blades bearing on the conductive part of said housing.

 According to another aspect of the invention, said metal mesh comprises a part projecting from the material making up said transparent cover on the four edges thereof, said parts being able to be folded to form spring blades resting on the conductive part of the housing .

 According to one embodiment, said conductive element comprises a thin layer of transparent electrically conductive material deposited on the surface and on the edge of said transparent cover.

 According to another embodiment, said conductive element comprises a deposit of fine and intertwined strips of electrically conductive material forming a grid on the surface of said transparent cover.

 According to one aspect of the invention, the mesh size of said mesh is at most 7.5 millimeters.

 According to another aspect of the invention, said means for bringing the electrically conductive element of the transparent cover into contact with the housing of the device comprises depositing a layer of electrically conductive adhesive on the edge of said transparent cover making it possible to maintain it in contact with said device housing.

 According to another embodiment, said conductive element comprises a thin layer of transparent electrically conductive material deposited on the surface of said envelope of the light source.

 According to another aspect of the invention, said means of contact between the electrically conductive element of the envelope and an electrically conductive cavity enclosing the supply of the source comprises cables shielded by an electrically conductive braid, said braid being electrically connected on the one hand to the electrically conductive layer of the envelope and on the other hand to the electrically conductive cavity enclosing the power supply.

 The invention also relates to a vehicle interior ceiling light comprising a light source of the neon or fluorescent tube type equipped with such a shielding device against electromagnetic disturbances.

 The invention also relates to a vehicle stop light comprising a light source of the neon or fluorescent tube type equipped with such a shielding device against electromagnetic disturbances.

Other characteristics and advantages of the invention will appear on reading the description of the embodiments, given below with reference to the appended drawings in which:
- Figure 1 is a longitudinal sectional view of a vehicle lighting device.

 - Figure 2 is a perspective view of the transparent cover of this device.

 - Figure 3 is an enlarged sectional view of a detail of Figure 1 showing the contact between the housing and the cover of the lighting device.

 - Figure 4 is a longitudinal sectional view of a vehicle lighting device illustrating another embodiment of the invention.

 - Figure 5 is an enlarged sectional view of a detail of Figure 4 showing the contact between the housing and the cover of the lighting device.

 - Figure 6 is an enlarged sectional view of a detail of Figure 4 showing another possible embodiment for the contact between the housing and the cover of the lighting device.

 - Figure 7 is a perspective view of the transparent cover of the lighting device according to another embodiment.

 - Figure 8 illustrates a method of grounding the housing on the vehicle body.

 - Figure 9 is a perspective view of a vehicle ceiling light produced according to the invention.

- Figure 10 is a sectional view of a lighting device according to another embodiment
- Figure 11 is an enlarged sectional view of a detail of Figure 10 illustrating the shielding continuity between the lamp and the shielded cable.

 - Figure 12 is an enlarged sectional view of a detail of Figure 10 illustrating the shielding continuity between the shielded cable and the conductive housing enclosing the ballast.

 Figures 1 to 3 show a first embodiment of the invention. More specifically, Figure 1 is a longitudinal sectional view of a raised brake light lamp, using as a light source a fluorescent tube 1, enclosed in a housing 2 provided with a transparent or translucent neck neck 3 A reflector 4 allows the light to be returned to the transparent cover 3. The light source is supplied by a ballast 5, which generates a stable discharge, and which is itself connected, by means of two cords 7 and 8, to the vehicle battery delivering a voltage of 12V.

This ballast is enclosed in a conductive cavity 6 ensuring a first shielding preventing the electromagnetic waves emitted by this supply from leaving the housing.

 In an embodiment not shown, the ballast is not enclosed in a clean cavity, it is the cavity, produced by the light housing and its cover according to the invention, which plays the role of shielding and serves to retain radiation from food.

 In the embodiment of Figure 1, the housing used is made of charged plastic material, for example a thermoplastic containing graphite particles, which is therefore electrically conductive in the mass. The material used for the housing can also be polyacetylene, a naturally conductive material.

 The transparent cover 3 comprises a metal mesh 9, made of aluminum or copper for example, which is included in the transparent thermoplastic material.

 FIG. 2 shows more explicitly the composition of this transparent cover: it comprises a first strip of transparent thermoplastic 12 on which a grid 9 is placed, the mesh size of which will be detailed below, and a second strip 13 of transparent thermoplastic molded onto the grid 9.

 The mesh size of the mesh 9 should be significantly less than the smallest wavelength of the electromagnetic emissions that one seeks to retain in the cavity. If one chooses to shield the device up to frequencies of 10 Ghz, while the standard in terms of electromagnetic compatibility CISPR / D WG2 secretariat 37 only requires shielding up to 1 Ghz, this corresponds to wavelengths d '' at least 3 centimeters.

 By taking meshes of size less than 7.5 millimeters, all the disturbing frequencies will be retained inside the fire. Generally, the mesh size of the grid will be at most L4 where X is the shortest wavelength of the disturbing radiation to be eliminated.

 It can be noted in FIG. 2 that a part of the metal mesh 9 protrudes from the thermoplastic blades 12 and 13 on each side of the cover. This is intended to ensure electrical contact between the electrically conductive box 2 and the electrically conductive element of the transparent cover formed here by the metal mesh 9.

 It is indeed very important to have good contact between the device housing and its transparent cover to ensure good shielding. In the embodiment described above, Figure 3 shows a detail of the contact between the housing 2 and the transparent cover 3. The part of the metal mesh 9 which protrudes is folded to form a leaf spring resting on the internal part of the housing. This contact is therefore elastic and has the advantage of not requiring very fine adjustment between the housing and its transparent cover.

 Figures 4 to 6 show a second embodiment of the invention. More specifically, FIG. 4 is a view in longitudinal section of a device for lighting the passenger compartment of a vehicle employing as a light source a fluorescent tube 1 enclosed in a housing 2 provided with a transparent or translucent cover. 3. It comprises, as in the embodiment described above, a reflector 4 and a ballast 5 supplying the light source connected to the vehicle battery by cords 7 and 8.

 In this embodiment, the box 2 is made electrically conductive by depositing, on the internal surface thereof, with a layer of aluminum for example, by a thick layer aluminizing process.

 In another fairly close embodiment, it is possible to deposit, on the internal surface of the housing 2, a layer of electrically conductive paint 10 such as, for example, silver or graphite paint.

 The electrically conductive element used for shielding the transparent cover will, in the embodiment of FIG. 4, consist of a thin layer 11 of transparent electrically conductive material, such as for example indium tin oxide, deposited on the surface of the transparent cover.

 Figure 5 shows a detail of the contact between the housing 2 and the transparent cover 3 in the embodiment described above. Here, a plane contact is made, under stress, between the electrically conductive layer 11 covering the transparent cover and the metal layer 10 covering the internal surface of the housing. This method is the simplest to carry out but it involves having a good surface condition of the electrically conductive layers 10 and 11.

 FIG. 6 proposes an embodiment making it possible to overcome this constraint concerning the surface states of the electrically conductive layers.

Indeed, a layer of electrically conductive glue 14 is added here, for example a silver glue, keeping the electrically conductive layers 10 and 11 firmly in contact covering the housing and the transparent cover.

 Of course, the two embodiments described in Figures 1 and 4 can be mixed.

That is to say that it is possible to use a box covered on its internal face with an electrically conductive layer with a transparent cover containing a metallic mesh. On the other hand, it is possible to marry a case of electrically conductive plastic material with a transparent cover covered with an electrically conductive layer.

 FIG. 7 illustrates another possible embodiment for inserting an electrically conductive element in the transparent cover of the lighting and / or signaling device. This is done by depositing thin strips of conductive material 15 on the surface of the transparent cover 3, on its internal or external face, according to a mesh size of less than 7.5 millimeters. This therefore forms an electrically conductive grid which does not allow any disturbing electromagnetic wavelength to pass. For the contact with the box 2, the methods illustrated in FIGS. 5 and 6 can be used.

It should be noted in this regard that the conductive material must also be deposited on the edge of the transparent cover to provide a sufficient contact area with the housing.

 FIG. 8 illustrates an example of grounding of the shielding on the bodywork. Shielding is not essential when all the radiating elements of the system are placed inside a completely electromagnetically sealed cavity. Grounding, however, improves current shielding because it prevents the shielding elements from becoming radiant in turn if current can flow, for example by capacitive coupling. In the embodiment of Figure 8, the shielded housing 17 is connected to the body 16 by an electrically conductive braid 22. The electrical contacts being ensured, at the housing by a screw 20 and a nut 21, and at the level of the bodywork by a screw 18 and a nut 19.

 FIG. 9 shows the case of a vehicle ceiling lamp produced according to the invention. The power supply and the connection wires are not shown in the figure.

The light source 23 is a fluorescent tube. The housing 24 and the transparent cover 26 are produced in accordance with the techniques described above, but in the present case, one of the walls of the cavity can be formed by the body itself 25. Thus, the earthing is directly made.

 In variants not shown in the previous examples, the conductive elements or conductive layers are arranged outside the housing.

 Figures 10 to 12 show a third embodiment of the invention. More specifically, FIG. 10 is a sectional view of a vehicle lighting device comprising an elongated light source 27 the envelope of which is, at least partially, transparent or translucent, fed by a ballast 29 which is connected to the battery by cords 31 and 32.

 In this embodiment, the ballast 29 is enclosed in a conductive housing 30 which can be produced, as described above, by depositing an electrically conductive layer on its surface or by using a conductive material in the mass.

 The electrically conductive element of the envelope of the light source 27 consists of a thin layer 28 of transparent electrically conductive material, such as for example indium tin oxide, deposited on the surface of the envelope of source. This embodiment makes it possible to have a smaller surface area to be covered than in the case where the layer of indium tin oxide is deposited on the transparent cover of the device, and therefore it allows the use of less oxide.

 The cables 33 and 34 ensuring the electrical connection between the ballast 29 and the source 27 must also be shielded by being enclosed in an electrically conductive braid according to a known embodiment.

 FIG. 11 shows a detail of the contact between the tube covered with its conductive layer 37 and the connection cable 38. The core of the cable 39 is connected directly to one of the supply terminals of the tube. The braid for shielding the cable 40 is electrically linked to the conductive layer of the tube by means of a conductive ring 41 and lug 42 assembly which is known in electronics. This ensures shielding continuity between the connection cable and the light source.

 Figure 12 shows a detail of the contact between the connection cable 43 and the ballast enclosed in its conductive housing 44. The core of the cable 45 is connected to the output terminal of the ballast. The shielding braid has a tongue 46 which is maintained in electrical contact with the conductive housing 44 by means of a screw and nut assembly 47. This makes it possible to ensure the shielding continuity between the connection cable and the conductive housing enclosing the ballast.

 In the case of this embodiment, the light source and the ballast supplying it are no longer necessarily in the same housing, which can have advantages if it is desired to have a less bulky housing containing only the light source.

Claims (12)

REVEWDICATIOS  1 - Lighting and / or signaling device for a motor vehicle, comprising a light source of the elongated tubular discharge lamp type (1) such as, for example, a neon tube or a fluorescent tube, the envelope of which is at least partially transparent; a housing (2) enclosing said light source; a power supply of said light source; and a transparent cover (3), allowing the exit of the light, characterized in that any one of the transparent envelope or cover elements comprises at least one electrically conductive element (9), and a means of contacting between this conductive element and respectively, an electrically conductive cavity enclosing the power supply of the source or the electrically conductive wall of said housing.  2 - Device according to claim 1 characterized in that said conductive element (9) comprises a metal mesh molded in the material of said transparent cover.  3 - Device according to claim 1 or 2 characterized in that said means for contacting between the electrically conductive element of the transparent cover (3) and the housing (2) of the device comprises a metal mesh (9), part of which protrudes of the material making up said transparent cover (3) on at least one edge thereof, said parts being able to be folded to form spring blades bearing on the conductive part of said housing.  4 - Device according to claim 3 characterized in that said metal mesh (9) has a portion projecting from the material of said transparent cover (3) on the four edges thereof, said portions being able to be folded to form spring blades s 'pressing on the conductive part of the housing (2).  5 - Device according to claim 1 characterized in that said conductive element comprises a thin layer of electrically conductive transparent material (11) deposited on the surface and on the edge of said transparent cover (3).  6 - Device according to claim 1 characterized in that said conductive element comprises a deposit of thin and intertwined strips (15) of electrically conductive material forming a grid on the surface of said transparent cover (3).  7 - Device according to claim 2 or claim 6 characterized in that the mesh size of said mesh (15) is at most 7.5 millimeters.  8 - Device according to claim 5 or 6 characterized in that said means for contacting between the electrically conductive element of the transparent cover (3) and the housing (2) of the device comprises depositing a layer of electrically conductive glue (14) on the edge of said transparent cover making it possible to keep it in contact with said device housing.  9 - Device according to claim 1 characterized in that said conductive element comprises a thin layer of transparent electrically conductive material (28) deposited on the surface of said envelope (27) of the light source.  10 - Device according to claim 1 or 9 characterized in that said contact means between the electrically conductive element (28) of the casing (27) and an electrically conductive cavity enclosing the supply of the source comprises cables shielded by an electrically conductive braid, said braid being electrically connected on the one hand to the electrically conductive layer of the envelope and on the other hand to the electrically conductive cavity enclosing the supply.  11 - Vehicle interior ceiling light characterized in that it comprises a lighting and / or signaling device according to one of the preceding claims.  12 - Vehicle stop light characterized in that it comprises a lighting and / or signaling device according to one of claims 1 to 10.