Patent Abstract:
A motor-vehicle headlight uses a gas-discharge lamp with a power-supply circuit, the lamp being mounted in a mirror. A screening device reduces interfering electromagnetic emissions. 
     The power-supply circuit is in a housing to the rear of the lamp, and the screening device has a conducting material entirely surrounding the housing and able to provide electrical continuity between a screening braid of a power-supply cable arriving at the said housing and screening arrangements which are associated with the mirror. 
     The invention also proposes a gas-discharge lamp incorporating such screening means.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates, in a general way, to headlights with a discharge lamp. 
     BACKGROUND OF THE INVENTION 
     Normally such a headlight comprises a reflector in which is mounted a discharge lamp, supplied with power by a separate high-voltage power-supply module, fixed, for example, in or onto the casing of the headlight. A screened cable links the power-supply module to the lamp, while the electromagnetic emissions in the region of the lamp and of its power-supply module are trapped by specific screening arrangements. 
     Discharge lamps have recently been developed characterized by having all or part of the high-voltage power-supply circuit present in a fixed or removable base of the lamp. Recourse is thus avoided to a power-supply casing housing the converter and high-voltage circuits, and therefore heavy and bulky, and difficult to place in a motor-vehicle headlight the requirements of which in terms of compactness and of lightness are constantly increasing. Hence, with this type of lamp, only one DC—DC converter circuit has to be provided separately from the lamp, with a substantially reduced weight and bulk. 
     One difficulty which can be expected with this new type of lamp, however, lies in the problems of electromagnetic compatibility as regards the power-supply circuits associated with the lamp. 
     Hence, in order to improve the electromagnetic compatibility all round the headlight, it may prove to be necessary to design the adjoining bodywork of the vehicle in such a way that it participates in the screening with respect to the stray electromagnetic emissions. 
     It will be understood that this will constitute an undesirable constraint on the constructors, given that they wish to preserve complete freedom in the design of the bodywork at the front of the vehicle. Such an approach is inapplicable, moreover, in the case of bodywork made of composite materials, or more generally non-conducting materials. 
     The present invention aims to overcome these problems of the prior art, and to propose a headlight which, in itself, without increasing the weight, complexity or cost price either of its casing or of other elements, and without having to design the adjacent bodywork in a specific way as regards these questions of interference, is able to satisfy the usual requirements in terms of electromagnetic compatibility. 
     SUMMARY OF THE INVENTION 
     To that end, according to a first aspect, it proposes a motor-vehicle headlight, comprising a gas-discharge lamp combined with a power-supply circuit and mounted in a mirror, and means of screening with respect to interfering electromagnetic emissions, characterized in that the said power-supply circuit is accommodated in a housing associated with the lamp to the rear thereof, and in that the screening means comprise a conducting material entirely surrounding the said housing and able to provide electrical continuity between a screening braid of a power-supply cable arriving at the said housing and screening arrangements which are associated with the mirror. 
     Preferred, but non-limiting, aspects of the headlight according to the invention are as follows: 
     the said conducting material belongs to a casing defining the said housing, 
     the said conducting material is mechanically fixed to the outside of the said casing, 
     the said conducting material is deposited on an outer face of the said casing, 
     the said conducting material belongs to a cover affixed to the rear of the mirror and surrounding a non-conducting casing defining the said housing, 
     the headlight comprises first linking means for ensuring electrical continuity between the said conducting material surrounding the said housing and a second, screening, conducting material provided at the rear surface of the mirror, 
     the first linking means comprise a series of clips electrically linked to the said second conducting material and bearing against the said first conducting material, 
     the said clips are mounted on a lamp holder affixed to the mirror, 
     the first linking means comprise arrangements for supporting the said cover against the said second conducting material at the rear of the mirror, 
     the first linking means comprise a deformable seal made of electrically conducting material, interposed between the first and second conducting materials, 
     the deformable seal is mounted on the mirror, 
     the deformable seal is mounted on a lamp holder affixed to the mirror, 
     the headlight comprises second linking means for ensuring electrical continuity between the said conducting material surrounding the said housing and the said screening braid, 
     the casing of the lamp possesses a first connector, the end of the power-supply cable possesses a second connector able to plug into the first connector, and, when the first and second connectors are separated, the said second linking means are able to break the electrical continuity between the said conducting material surrounding the said housing and the said screening braid only after the contacts of the first and second connectors carrying the power-supply voltage for the lamp have been separated, 
     the second linking means comprise a series of clips carried by the said second connector, the said clips being in contact with the screening braid and with the conducting material surrounding the casing, 
     the said second linking means comprise a conducting seal in contact with the screening braid and with the conducting material surrounding the casing, 
     an elastic means is provided for retaining the lamp in axial position, the said means bearing against the conducting, screening material, and the said elastic means, which is conducting and which, in retaining position, is in contact with the said screening braid of the cable, forms part of the said second linking means, 
     the said second linking means comprise arrangements for support against the braid of the power-supply cable, which are formed on the said cover around an orifice for the said cable to pass, 
     the headlight comprises a conducting elastic element able to bear against the said conducting material in the region of a rear face of the said casing, in order simultaneously to retain the lamp in axial direction and to provide electrical continuity for screening with other screening elements of the headlight, 
     the said housing forms an integral part of the lamp, 
     the said housing forms part of a connector on which the lamp is mounted removably, 
     the headlight further comprises control circuits accommodated in an electrically conducting control box situated at a distance from the lamp, and third linking means for ensuring electrical continuity between the said control box and the braid of the cable, 
     the third linking means comprise a third connector provided on the control box and a fourth connector provided at the end of the power-supply cable opposite to the lamp and able to be plugged into the third connector, and, when the third and fourth connectors are separated, the said third linking means are able to break the electrical continuity between the said control box and the said screening braid only after the contacts of the third and fourth connectors carrying the power-supply voltage for the lamp have been separated. 
     According to a second aspect, the present invention proposes a gas-discharge lamp for a motor-vehicle headlight, the said lamp being combined with a power-supply circuit, characterized in that it incorporates the said power-supply circuit in a housing, and in that it further comprises screening means comprising a conducting material entirely surrounding the said housing and able to ensure electrical continuity between a screening braid of a power-supply cable arriving in the housing and screening arrangements provided on a mirror able to accommodate the said lamp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects, objects and advantages of the present invention will emerge better on reading the following detailed description of various embodiments thereof, given by way of non-limiting example and by reference to the attached drawings, in which: 
     FIG. 1 is a side view of a discharge lamp according to a first embodiment of the invention, 
     FIG. 2 is a back view of the lamp of FIG. 1, 
     FIG. 3 is a side view, partially in section, of the lamp of FIGS. 1 and 2, 
     FIG. 4 is a back view, partially in section, of the lamp of FIGS. 1 to  3 , 
     FIG. 5 is a side view, partially in section, of a lamp/mirror assembly according to a second embodiment of the invention, 
     FIG. 6 is a side view, partially in section, of the mounting of a lamp according to the first embodiment of the invention in a mirror of the headlight, 
     FIG. 7 is a partial back view illustrating a detail of the mounting of FIG. 6, 
     FIG. 8 is a view in partial section illustrating the mounting of FIG. 7 in more detail, 
     FIG. 9 is a back view of a lamp holder used in the mounting of FIG. 8, 
     FIG. 10 illustrates a means for screening continuity between lamp and cable used with a lamp according to the invention, 
     FIG. 11 is a side view, partially in section, of a variant of the lamp/mirror assembly of FIG. 5, 
     FIG. 12 is a side view, partially in section, illustrating a means for screening continuity between lamp and cable used with a lamp according to the invention, and 
     FIG. 13 is a diagrammatic back view of a rear cap of a mirror capable of being used in the second embodiment of the invention. 
     FIG. 14 is a side view, partially in section, of a lamp/mirror assembly, as shown in FIG. 5, further illustrating conductive links between a control box and a screened cable. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the various figures, like reference numerals refer to like parts. 
     By reference first of all to FIGS. 1 to  4 , a discharge lamp  10  has been represented which comprises an outer bulb  11 , sheltering—in a way which is not illustrated and known in itself—an inner bulb holding a gaseous mixture and two electrodes in order to form a luminescent arc via a gas-discharge phenomenon. 
     To the rear of the bulb  11  extends a lamp body  12  possessing a collar  13  intended to co-operate with appropriate support parts of the mirror so as to reference the position of the lamp therein, this body being extended to the rear by a casing  14  formed, for example, in a single piece with the body, the whole being made of appropriate plastic, and defining a cavity  15  intended to shield the electronic circuits (not represented) making it possible to supply power to the lamp at the appropriate voltages. This casing  14  defines, at its lower part, a connector  17  able to cooperate with a complementary connector (not illustrated) at the end of a screened cable for supplying power to the lamp  10 , supplying a voltage, preferably a DC voltage higher than that of the on-board network of the vehicle, produced by an appropriate DC/DC converter, and processed in an appropriate way by the power-supply circuits. 
     It will be observed here that the present invention applies equally well to a lamp in which the casing is affixed removably, by means of an appropriate connector, at the rear of the lamp. 
     According to a first embodiment of the invention, and as illustrated in FIGS. 3 and 4, the casing  14  for the power-supply circuits receives an essentially continuous conducting outer envelope  16  intended to trap the stray electromagnetic emissions emitted by these circuits, so as to perfect the screening to which, in a way which is known in itself, the mirror of the headlight and a metal shade placed in the mirror in front of the lamp already contribute. 
     According to a first implementation, this envelope  16  is produced in the form of a thin metal sheet affixed around the casing  14 . 
     According to a second implementation, this envelope is produced by deposition, especially by chemical or physical means, of at least one conducting layer  16  on the outer face of the casing. According to one variant, provision can be made to form this deposition on the inner face of the casing, auxiliary conducting means being provided in this case so that the continuity of the screening with the other parts of the headlight, external to this casing, can be achieved. 
     It will be observed that the thin envelope is extended, at  16   a , in the region of the connector  17 , so as to leave accessible strictly only what is necessary to provide for the connector  17  to interact with its complementary connector. 
     FIG. 5 illustrates the principle of a second embodiment of the invention. In this figure, the lamp  10  produced as before has been illustrated, but with a casing  14  itself devoid of screening, a mirror  20  in which the lamp is mounted, and a metal shade  40 . The mirror  20 , on its rear face opposite its reflecting surface  21 , possesses a conducting layer  22  affixed mechanically or deposited by physical or chemical means. This conducting layer  22  and the shade  40  are both, in a way which is known in itself, connected to earth in order to participate in the screening with respect to interfering electromagnetic emissions, principally as regards the arc and the electrodes of the lamp. 
     Also represented in FIG. 5 is a power-supply cable  50 , provided with a bare, outer screening braid  51  and terminating in a connector  52  able to interact with the connector  17  provided on the casing  14  of the lamp. This cable, at its other end, preferably possesses a similar connector, capable of ensuring, under the same conditions, continuity of the screening with an earthed conducting casing sheltering the above mentioned DC—DC converter and, more generally, control circuits of the headlight. 
     According to the second embodiment of the invention, the casing  14  of the lamp, which protrudes from the rear of the mirror, is accommodated within a conducting cover  30  affixed to the rear of the mirror. 
     This cover possesses a main wall  31  situated face-to-face with the rear face and the side and upper and lower faces of the casing  14 , while, at its open front end (to the right in FIG.  5 ), it features peripheral arrangements, such as bends  32  or clips, intended to provide electrical continuity with the conducting layer  22  of the mirror. 
     In a variant, or additionally, it is possible to interpose between the front end of the cover  30  and the rear face of the mirror possessing the conducting layer  22  a deformable seal made of electrically conducting material, which can be mounted either on the cover or on the mirror. 
     The cover  30  also possesses an aperture, in the region of its lower wall, surrounded by arrangements  33  such as clips, able to provide electrical contact with the bare screening braid  51  of the cable  50 . Here again, a conducting seal can be used. 
     It will be observed here that it is the cover  30  which provides the electrical continuity between the earthed screening elements constituted by the braid  51  and by the conducting layer  22  of the mirror  20 , while the shade  40  is linked to the conducting layer  22  by conducting support lugs, not represented. 
     FIGS. 6 to  9  illustrate one possible embodiment for mounting the lamp as described above by reference to FIGS. 1 to  4  in a mirror. 
     Here the mirror possesses, either in a single piece, or affixed to it, a bell-shaped element  23  extending to the rear of the mirror around the lamp hole and open to the rear. 
     The lamp is mounted in the mirror through the rear in such a way that its casing  14 , with conducting outer layer  16 , comes to be engaged partially in the bell  23 . 
     This bell carries, at its periphery, a plurality of metal clips  231  having appropriate elasticity properties, and made of spring steel, for example, which are able, when the lamp is put in place, to come to bear against the conducting layer  16  of the casing  14 . 
     These clips are linked electrically, moreover, to the conducting layer  22  situated at the rear of the mirror  20 , in order thus to ensure electrical continuity of the screening between the mirror and the casing  14  of the lamp. 
     Moreover, means are advantageously provided on the bell  23  for retaining the lamp  10  in position, which consist of a leaf spring  232  or other elastic element, one end of which is mounted so as to be articulated onto the said bell and the opposite end of which can be latched on to the latter on the opposite side. In this position, the leaf spring  232  bears on the rear face of the casing  14  so as to retain the lamp in its reference position defined by the support of the collar  13  on appropriate arrangements surrounding the lamp hole of the mirror. It will be noted here that the leaf spring  232  also contributes to the electrical continuity of the screening. 
     FIG. 8, in particular, illustrates the pivoting mounting of the leaf spring  232  at its end  2321 , and the latching of the said leaf spring at its opposite end  2322 . 
     Furthermore, FIG. 8 also shows that the clips  231  are extended forwards (that is to say downwards on the figure) so as to meet up with a conducting piece  60  belonging to the lamp holder, which is engaged in the lamp hole of the mirror and in contact both with the conducting layer  22  of the mirror and with the shade  40  (not represented) by means of fixing lugs thereof (also not represented). 
     FIG. 9 for its part illustrates the lamp holder PL as a whole, carrying four clips  231  and provided with respective arrangements  61 ,  62  for the pivoting mounting of the retaining leaf spring  232  and for its fastening in latched position. 
     In a variant of the various forms of clips described above, or in addition to them, one or more deformable seals made of electrically conducting material can be used, which are able to be compressed between the conducting surfaces between which the electrical continuity has to be ensured. 
     FIG. 10 diagrammatically represents, in perspective, the interaction between the connector  17  belonging to the casing  14  of the lamp and the complementary connector  52  provided at the end of the screened power-supply cable. 
     Thus, the body of this complementary connector  52  carries a series of elastic and electrically conducting clips  521  able to come to bear, when the connectors are assembled, against the conducting layer  16   a  surrounding the connector  17 . The electrical continuity of the screening is thus ensured between the outer braid  51  of the cable  50  and the conducting coating  16 ,  16   a  of the lamp casing  14 , and, as a consequence, with the other elements, mainly mirror and shade, participating in the screening. 
     Here again, the clips  521  can be replaced or supplemented by a deformable seal made of electrically conducting material compressed between the surfaces between which the electrical continuity of screening has to be ensured. 
     It will be noted here that, advantageously, the connectors  17  and  52  are designed such that disconnecting them first of all causes disconnection of the conductor or conductors carrying the power-supply voltage for the lamp, and, only then, disconnection of the link providing the continuity of the screening. Conversely, when the connectors  17  and  52  are assembled, the continuity of the screening will be established before the power-supply connector or connectors proper. 
     In the same way, it is advantageous for the connectors present between the opposite end of the cable  50  and the control box belonging to the headlight and situated remotely from the lamp to exhibit the same behavior. 
     FIG. 11 for its part illustrates another implementation for mounting a lamp according to FIGS. 1 to  4  at the rear of the mirror  20 . 
     The lamp hole is surrounded by an axial collar  24  and a conducting crown ring  25  is mounted, for example by screws, on to the free annular surface defined by the collar  24  at its rear end. 
     This crown ring  25  carries, at its periphery, a series of double clips  251  a forward part of which is able to come into contact with the conducting layer  22  formed at the rear of the mirror  20  (this conducting layer being extended at  22   a  in the region of the outer face of the collar  24 ), and a rear part of which is able to come into contact with the conducting coating  16  formed on the casing  14  of the lamp  10 . Here again a conducting seal can be used. 
     Moreover, the crown ring  25  carries a leaf spring  252  for retaining the lamp, similar to the leaf spring  232  described above. 
     Here again, the electrical continuity is ensured between the screening  16  of the casing  14  of the lamp and the screening  22  of the mirror. 
     FIG. 12 for its part illustrates an improvement to the retaining leaf spring  242 , here mounted directly on a collar  24  produced in a single piece with the mirror  20  or else affixed onto it. According to this improvement, the leaf spring  242  carries an appendage  2421  intended to cover over, with electrical conduction, the bare outer braid of the power-supply cable  50 . This especially makes it possible to achieve electrical continuity between the said braid and the screening  22  of the mirror  20 , the electrical continuity of which with the leaf spring  242  is achieved by any appropriate means. 
     FIG. 13 illustrates a particular embodiment of the mounting of the screening cover  30  of FIG. 5 around the rear part of the lamp. The cover  30  possesses a first appendage  34  by which it is mounted so as to pivot on a spindle integral with the mirror, and a second appendage by which, with the cover being in place covering over the lamp, it is held in position with the aid of a screw or the like. 
     Finally, FIG. 14 is a side view, partially in section, of a lamp/mirror assembly, as shown in FIG. 5, and further illustrates features of the invention described above. FIG. 14 shows an earthed conducting casing or control box  531 , which shelters a DC—DC converter and, more generally, additional control circuits of the headlight. The conducting casing  531  can be connected to the screening braid  51  near one end of the power supply cable  50  via connectors  532  and  533 , which ensure electrical conductivity between the screening braid  51  and the conducting casing  531 . 
     Clearly, the present invention is not in any way limited to the embodiments described and represented, but the person skilled in the art will be able to contribute numerous variants and modifications.

Technology Classification (CPC): 5