GB2070755A

GB2070755A - Lamp in particular for motor vehicles

Info

Publication number: GB2070755A
Application number: GB8105060A
Authority: GB
Original assignee: Equipements Automobiles Marchal SA
Current assignee: Equipements Automobiles Marchal SA
Priority date: 1980-02-29
Filing date: 1981-02-18
Publication date: 1981-09-09
Also published as: FR2487040B1; GB2070755B; JPS6340322B2; FR2487040A1; IT1144126B; ES265281U; ES265281Y; JPS5761201A; DE3107420A1; IT8167279A0

Abstract

An automobile headlight has a plastic headlamp glass (1), sealed (at 3) to a primary reflector (2) moulded of a polycarbonate material. The primary reflector is protected against the disadvantageous effects of overheating (e.g. softening and deformation) by the presence of an aluminium secondary reflector (9) surrounding the light bulb (20) and defining a "visor" (9b) shielding the top of the primary reflector (2). Air flow passages (16) exist to permit air circulation within the headlight to equalise temperatures between the hot secondary reflector (9), the cold headlamp glass (1), and the temperature-sensitive primary reflector (2). <IMAGE>

Description

SPECIFICATION Lamp in particular for motor vehicles The present invention relates to a lamp, and in particular to a lamp which may be used for the front lighting of a motor vehicle.

It is known that a headlight of a motor vehicle generally consists of a reflector of a paraboloid shape called a "parabolic reflector" whose front part is closed by a diffuser glass and whose back part is fitted with a bulb fitted near the reflector apex by means of a bulb holder. According to a conventional manufacturing technique, the parabolic reflectors are obtained by stamping a metal sheet.

It has been proposed to replace these metal reflector designs by designs using a plastic material. This recent technique makes it possible to benefit simultaneously from several advantages, that is to say, on the one hand, a reduction in weight and on the other hand, a reduction in cost which is all the greater since the reflector shapes are more complicated.

Unfortunately, this technique has a drawback which is by no means negligible in the poor behaviour of current plastics materials at high temperatures. Now, in view of the lighting power requirements, the temperature in the hottest zones of parabolic reflectors may rise to 1 50 or 200"C which entails a softening and deformation for the thermoplastic materials. Any deformation of the reflector has, of course, the effect of modifying the reflected beam so that, in the absence of special precautions, the use of thermoplastic materials does not allow conformation with the lighting standards which are imposed in particular for the "dipped" beam.Thermosetting plastic materials such as polysulphones are, of course, known to be capable of resisting the temperatures imposed on the reflector but these plastic materials are expensive and, if they are used, the expected improvement in cost from the use of plastic materials disappears.

In French Patent 2 242 638, it has been proposed to make a motor vehicle headlight by using a reflector constituted by two different parts joined to each other: the rear part which is near the light bulb is made of an expensive plastic material with a good thermal stability: the front part which is subjected to less overheating is made of a cheap thermoplastic material. Such a headlight, constituted by a reflector made in two parts, allows the lighting standards to be observed and may be produced at a relatively low cost. However, in practice the joining of the two parts of the reflector is effected in a plane along a line, all points of which must be at a temperature which can be withstood by the plastic material having the lower thermal stability.However, since the rear part of the reflector necessarily has a relatively large surface, this constitutes an adverse element as regards keeping down the cost.

The object of the present invention is to propose a motor vehicle headlight whose structure utilises to a large extent plastic materials having relatively poor thermal characteristics, thereby making it possible to reduce the cost, while making it possible to avoid any deformation of the plastic materials due to softening of the headlight in use.

According to the present invention we provide a headlight comprising a primary reflector whose front part is closed by a front pane and made of a material having a low thermal stability; and a secondary reflector disposed within the primary reflector and made of a material having a thermal stability better than that of the primary reflector; wherein said secondary reflector has its focus substantially coincident with that of the primary reflector, the secondary reflector and the primary reflector are connected at the opening of the apex zone of the primary reflector, the said opening is adapted to accommodate the light source with the rear part of the light source surrounded over its whole circumference by the said secondary reflector, and the front edge of the secondary reflector is defined so that the secondary reflector constitutes a thermal shield for those zones of the primary reflector which, in the absence of the secondary reflector, would have been the most overheated zones.The external reflector, called "the primary reflector" may be constituted by a plastic material which is sensitive to heat and is protected by the internal reflector called "the secondary reflector" which constitutes a thermal shield for the external reflector in the zones where the overheating of the primary reflector would have the greatest tendency to manifest itself in the absence of the secondary reflector. The secondary reflector is thus located in the vicinity of the light source, for example a light bulb, and must, of source, be capable of withstanding a considerable rise in temperature; this is the reason why provision has been made to make the secondary reflector either of metal, in which case it may be stamped or moulded, or of a plastic material in which case the plastic material used must have very favourable heat resisting characteristics.The secondary reflector, being placed nearer the light source than the primary reflector, has its surface smaller than the corresponding protected surface of the primary protector and it is thus possible to obtain, with a smaller quantity of an expensive material, the same result as when the single plastic reflector was made of two joined parts. Moreover, a shape may be adopted for the secondary reflector which is strictly adapted to the temperature profile found on the external reflector, so that the front edge of the secondary reflector may have a shape which is complicated to a small or greater extent, whereas in the case where a front part and a rear part of the same headlight were joined, the joint had to be practically effected in one plane; this circumstance again affords a maximum economy in the use of expensive materials constituting the secondary reflector.This latter advantage is particularly striking for the making of headlights whose external parabolic reflector is bounded by two parallel planes arranged horizontally when the headlight is placed into position in the vehicle. In fact, when the headlights are on "dipped beam" all the light emitted by the headlight is directed on the top part of the parabolic reflector which gives rise to a beam deflected towards the ground in order to avoid blinding the drivers of oncoming vehicles. Now, the top plane delimiting the reflector is, by reason of the rectangular shape of the front pane (the so-called "headlamp glass"), extremely near the light source; this results in a particularly noticeable overheating of the top part of the reflector of a headlight of this type.If the headlight is in accordance with the present invention, the secondary reflector may comprise, at its top part, an extension forming a visor and constituting a thermal shield for the top part of the primary reflector which is normally subjected to undue overheating; the making of this visor only slightly increases the surface of the secondary reflector since the edges of the said visor may be defined in an accurate manner on the basis of thermal plottings carried out on the external reflector which allows the surface of the secondary reflector, and hence the quantity of material to be used for constituting this reflector, to be limited precisely to the necessary amount.

The implementation of the present invention makes it possible to benefit from several advantages which derive from the adopted structure.

Firstly, the secondary reflector disposed within the primary reflector is defined by a parabola having a slightly shorter focal length than that of the primary reflector; the axes as well as the foci of the two parabolas are identical; it follows therefrom that the solid angle of the light emission recovered and reflected by the secondary reflector is slightly greater than the corresponding angle in the case where the primary reflector is used on its own: this results in an improvement of the lighting characteristics of the headlight according to the invention for the same power consumed by the light source.

Secondly, the secondary reflector may easily comprise, on its reflecting surface, parallel striations arranged in vertical planes when the headlight is in place on the vehicle. This particular structure, already described in French Patent 758 501, allows a beam concentration to be avoided in the central zone of the headlamp glass by ensuring a certain diffusion of the light and in this way, one may use headlamp glasses made of a plastic material without risking any deformation of the central zone of said plastic headlamp glass.

This arrangement of the striations is particularly easy on the secondary reflector because of its small surface.

Thirdly, the thermal stability (i.e. mechanical heat resisting ability), of the headlight according to the invention, may be further improved by making provision for air circulation between the primary reflector and the secondary reflector. In.fact, the secondary reflector may be fixed 'on the primary reflector in the apex zone of the latter and it is easy to arrange openings for air circulation in the fixing zone to cause the front and rear parts to communicate via the annular space comprised between the two reflectors. Thus movement of air is ensured within the headlight so that the air is cooled on the headlamp glass and is reheated on the hot parts of the secondary reflector; this circulation ensures equalisation of the temperatures, and hence further improves the thermal stability of the headlight reflectors.

In French Patent 1 310 630, there has already been described a headlight comprising, on the one hand, a primary reflector which has its front part closed by a front pane or headlamp glass and is made of a material having a low thermal stability and, on the other hand, a secondary reflector arranged within the primary reflector and made of a material having good thermal stability, the secondary reflector having substantially the same focus and the same axis as the primary reflector. However, the rear part of this prior art light bulb, which is one of the zones which is most exposed to the heat, is not surrounded by the secondary reflector.In the present invention, not only is the rear part of the light bulb surrounded along the whole of its periphery by the secondary reflector, but the presence of the opening arranged in the rear part of the primary reflector for accommodating the light bulb is furthermore profitably used to ensure the connection between the primary reflector and the secondary reflector in this region.

In the present specification and the corresponding claims, the "front" of the headlight designates the part which is next to the front pane (i.e. the "headlamp glass"), and the "rear" of the headlight designates the part which is in the vicinity of the apex of the primary reflector.

In a preferred embodiment, the secondary reflector comprises at its top part an extension constituting a projection towards the front of the headlight; the secondary reflector has, on the one hand, a first zone of revolution at right angles to the filament of a said source surrounding the light source, and on the other hand a second zone of revolution which extends further than the first zone towards the front of the headlight through a minimum angle of 40 subtended at the axis of the headlights, this second zone of revolution defining the said projection; the fixing zone of the secondary reflector may be fixed within the primary reflector at a zone which includes openings ensuring a passage of air between the rear and the front of the primary reflector via the annular space comprised between the two reflectors; in a first variant the secondary reflector is made of metal, for example aluminium or magnesium, while in a second variant it is made of a heat-resisting plastic material, for example polysulphone; the secondary reflector may comprise over at least a part of its reflecting surface, striations disposed in substantially parallel planes, these striations being vertical when the headlight is installed in the vehicle; the opening at the apex of the primary reflector is extended by a cylindrical collar coaxial with the primary and secondary reflectors, said collar comprising at its end away from the connection zone with the primary reflector, a multiplicity of radial fins constituting axial stops for a complementary number of bosses which project radially outwardly of a sleeve carried by the secondary reflector in its apex zone, said bosses ensuring the centering of the said sleeve within the collar, the openings for the passage of air being defined between the various boss-fin pairs; the sleeve of the secondary reflector comprises a continuous or discontinuous rib, and a resilient ring is positioned between the said rib and the fins of the primary reflector to support the bosses resiliently on the fins; the sleeve defines internally a cylindrical housing intended to accommodate a holder for the light source; and the primary reflector may be delimited by two planes which are parallel to each other and parallel to the axis of the reflector, these two planes being horizontal when the headlight is installed in the vehicle; the headlamp glass or front pane is made of a plastic material.

To render the invention more readily understood, there will now be described an embodiment represented in the attached drawings by way of a purely illustrative and non-restrictive example. In these drawings: Figure 1 shows a vertical cross section, of a headlight according to the invention fitted with its bulb holder and its bulb, taken on a plane passing through the headlight beam axis, the said plane of section being marked I-I on Fig. 2; Figure 2 shows a horizontal cross section of the headlight of Fig. 1 taken along ll-ll of Fig. 1, the bulb holder being withdrawn; Figure 3 shows a front view of the headlight, taken on line Ill-Ill of Fig. 1, the bulb holder being withdrawn; Figure 4 shows a cross section along line IV-IV of Fig. 1, the bulb holder being withdrawn; and Figure 5 shows a cross section along the line V-V of Fig. 4, the bulb holder being withdrawn.

Referring to the drawing, there will be seen the front pane 1 of the headlight according to the invention this component 1 is normally referred to as the "headlamp glass", but is in this case formed of a transparent plastics material. Headlamp glass 1 closes off the front of a primary reflector 2 which constitutes the external reflector of the headlight. To ensure a good seal, the attachment of headlamp glass 1 on reflector 2 is effected via a sealing ring 3. As is clearly visible in Fig. 3, the headlamp glass 1 has a substantially rectangular shape. It is obtained by the moulding of a polycarbonate; the primary parabolic reflector 2 is obtained by the moulding of a thermoplastic polyester material.

The primary reflector 2 is delimited by two horizontal planes which are substantially symmetrical in relation to the optical axis of the headlight (coincident with the section lines ll-ll in Fig. 1 and i-l in Fig. 2). Near its apex, the paraboloid portion of the reflector 2 is truncated by a wall 4 which is perpendicular to the paraboloid axis, the said wall 4 comprising at its centre a circular opening which is continued rearwardly by a cylindrical collar 5. Collar 5 is surrounded by an outer, rearwardly extending protective cylindrical wall 6 coaxial with the collar 5, the said cylindrical wall 6 serving to support a closing stopper 6a which ensures the rear seal of the primary reflector 2.At its rear end, sleeve 5 comprises towards its axis three radial fins regularly distributed on its circumference and designated by 7 in the drawing. Moreover, sleeve 5 comprises internally, parallel to its axis, a rib 8 (Fig. 4).

Within the primary reflector 2, there has been arranged a secondary reflector generally designated 9. Reflector 9 has the same axis and the same focus as reflector 2. Its focal length is slightly shorter than that of the primary reflector 2; the focal length of the primary reflector is 25 mm whilst the focal length of the secondary reflector is 20 mm.

The filament of a light bulb 20 is arranged substantially at the common focus of the two reflectors 2 and 9. The secondary reflector 9 is extended towards the rear of the headlight by a cylindrical sleeve 10 comprising three bosses 11 projecting radially from its external surface and regularly distributed over its circumference. The bosses 11 constitute, by their peripheral lateral edge, the means for centering the sleeve 10 within collar 5. When the secondary reflector 9 is positioned in front, and when sleeve 10 is inserted in collar 5, bosses 11 come to be centred in the inner housing defined by collar 5 and come to bear axially on fins 7. Air passage openings 1 6 exist between the various pairs comprising a fin 7 and the associated boss 11 within the space comprised between the sleeve 10 and collar 5.The arrows shown in Fig. 1 indicate the direction of the air circulation within the headlight during its operation. The orientation of secondary reflector 9 in relation to primary reflector 2 around their common axis is ensured by the cooperation of the rib 8 with a corresponding groove 1 2 (Fig. 4) cut into the external surface of sleeve 10. The bosses 11 are held in abutment with the fins 7 by inserting a resilient ring or circlip 1 3 between fins 7 and a rib 14 cut out on the outside of sleeve 10 rearwardly beyond bosses 11. Rib 14 is disposed along a circular arc with a sufficiently small angular clearance for rib 14 to be able to pass between two consecutive fins 11.Thus the resilient ring 1 3 holds the secondary reflector 9 in its axial position in relation to primary reflector 2, and rib 8 ensures the angular positioning of the secondary reflector 9 in relation to the primary reflector 2 around their common axis.

Within sleeve 10, there is positioned a bulb holder 1 9 which supports the bulb 20 of the headlight. The bulb holder 1 9 abuts against a step 18 which projects into the housing defined internally by sleeve 1 0. The bulb holder 1 9 is maintained in abutment on step 18 by a spring clip 1 7 in a known way.

The secondary reflector 9 is moulded, i.e.

cast, of aluminium. Its reflecting surface directed towards bulb 20 comprises striations which are all disposed in vertical planes as may be clearly seen in Fig. 2. This arrangement makes it possible to avoid a concentration of the light beams on the central zone of the headlamp glass 1 so that the headlamp glass, although made of a plastic material, does not sustain any deformation since the hot spot which usually appears in its central zone is avoided. Forming the striations 9a of reflector 9 does not present any particular difficulties in view of the small dimensions of the said reflector 9. In fact, the secondary reflector 9 is bounded towards the front by a vertical plane at a short distance from the common focus of the two reflectors 2 and 9.

Yet secondary reflector 9 has, on its top part, an extension 9bwhich projects towards the headlamp glass 1 and is extended upwardly to the vicinity of the upper horizontal plane of the primary reflector 2. As shown in Fig. 3, the extension 9b is substantially symmetrical in relation to a vertical plane passing through the optical axis of the headlight and it is laterally delimited by planes passing through the said optical axis and forming an angle of 40 with the vertical plane of symmetry of extension 9b. The extension 9bthus has the shape of a visor forming a projection ahead of the cup-shaped zone of secondary reflector 9 which surrounds the bulb 20. Of course, the whole reflecting surface of secondary reflector 9 is a generally paraboloidal surface.

When the above described headlight is in operation, bulb 20 emits light rays on the two reflectors 2 and 9 and there heating of the reflecting surfaces will occur. Yet the secondary reflector 9 serves as a protective shield for primary reflector 2 and the shape of the front edge of the secondary reflector 9 is such that a protective heat shield is provided for all those zones of the primary reflector 2 which, in the absence of the secondary reflector 9, would be subject to overheating to an extent which cannot be withstood by the plastic material constituting primary reflector 2.Thus the presence of the secondary reflector 9 ensures the thermal stability (i.e. non-deformation) of the plastic material constituting primary reflector 2; in particular, the extension 9b protects the top part of primary reflector 2, which is more especially overheated when the headlight is working on a "dipped beam".

Moreover, the clearances subsisting between the sleeve 10 and the collar 5 communicate on the one hand the gap between the two reflectors 2 and 9 and on the other hand, the atmosphere at the back of the primary reflector 2, thanks to the passages 1 6 existing between two consecutive fins 7. It follows that within the annular space separating the two reflectors, there is established an air circulation which improves the thermal stability of the headlight since the air circulating in the headlight is cooled on the headlamp glass 1 and since the circulation tends to equalise the temperatures throughout the headlight.

Claims

1. A headlight comprising a primary reflector whose front part is closed by a front pane and made of a material having a low thermal stability; and a secondary reflector disposed within the primary reflector and made of a material having a thermal stability better than that of the primary reflector; wherein said secondary reflector has its focus substantially coincident with that of the primary reflector, the secondary reflector and the primary reflector are connected at the opening of the apex zone of the primary reflector, the said opening is adapted to accommodate the light source with the rear part of the light source surrounded over its whole circumference by the said secondary reflector, and the front edge of the secondary reflector is defined so that the secondary reflector constitutes a thermal shield for those zones of the primary reflector which, in the absence of the secondary reflector, would have been the most overheated zones.

2. A headlight according to claim 1, wherein the secondary reflector comprises in its top part an extension constituting a projection towards the front of the headlight.

3. A headlight according to claim 2, wherein the secondary reflector has, on the one hand, a first zone of revolution at right angles to the filament of a said light source, which first zone of revolution surrounds the light source and, on the other hand, a second zone of revolution which extends further than the first zone towards the front of the headlight throughout a minimum angle of 40 subtended at the axis of the headlamp, this second zone of revolution defining said projection.

4. A headlight according to any one of claims 1 to 3, wherein the secondary reflector is fixed on the primary reflector at a zone which includes openings ensuring a passage of air between the primary reflector and the secondary reflector.

5. A headlight according to any one of claims 1 to 4, wherein the opening at the apex of the primary reflector is continued by a cylindrical collar coaxial with the primary and secondary reflectors, said collar comprising at its end away from its connection with the secondary reflector a plurality of radial fins constituting axial stops for a complementary plurality of bosses which project radially outwardly of a sleeve carried by the secondary reflector in its apex zone, said bosses ensuring centering of the said sleeve in the collar.

6. A headlight according to claim 5, wherein said sleeve carried by the secondary reflector comprises on the outside a rib and wherein a resilient ring is positioned between said rib and the fins of the primary reflector to bias said bosses resiliently against the fins.

7. A headlight according to claim 6, wherein said rib on the outside of said sleeve is discontinuous.

8. A headlight according to any one of claims 5 to 7, wherein the sleeve internally defines a cylindrical housing intended to accommodate a bulb holder and wherein said light source is a light bulb inserted in said bulb holder.

9. A headlight according to any one of claims 1 to 8, wherein the primary reflector is delimited by two planes which are parallel to each other and parallel to the axis of the primary reflector, these two planes being horizontal when the headlight is placed in position in an automobile vehicle.

1 0. A headlight according to any one of claims 1 to 9, wherein the secondary reflector is made of metal.

11. A headlight according to any one of claims 1 to 9, wherein the secondary reflector is made of a heat resisting plastic material.

1 2. A headlight according to claim 10 wherein said metal is aluminium and said primary reflector is moulded of a polycarbonate material.

1 3. A headlight substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

1 4. An automobile vehicle including at last one headlight according to any one of the preceding claims.