FR2475186A1 - IMPROVEMENTS IN PLASTIC REFLECTORS FOR MOTOR VEHICLE HEADLAMPS - Google Patents

Abstract

THE INVENTION CONCERNS A PLASTIC MATERIAL REFLECTOR FOR A MOTOR VEHICLE HEADLIGHT, INTENDED TO COOPERATE WITH A LIGHT SOURCE TO OBTAIN A DETERMINED LIGHT BEAM. THIS REFLECTOR IS CHARACTERIZED IN THAT IT CONSTRUCTS BY CONSTRUCTION, AT LEAST IN ITS UPPER REGION OF GREATEST HEATING, A SURFACE SHAPE ZI SUBSTANTIALLY DIFFERING FROM THE OPTICAL SHAPE P NECESSARY FOR THIS EFFECT, BUT WHICH, UNDER THE CONDITIONS OF HEATING, CORRESPONDING TO NORMAL OPERATION OF THE PROJECTOR, DEFORMS SO THAT THE SAID INTERNAL SURFACE RETURNS TO THE SURFACE OPTICALLY NECESSARY FOR THE PRODUCTION OF THE DETERMINED BEAM. THIS IS A NEW SOLUTION TO THE PROBLEM OF HEATING OF PLASTIC REFLECTORS.

Description

The present invention relates to reflectors for projection

  motor vehicle engines made of plastics.

  In the construction of headlamps for motor vehicles

  For a long time it has been proposed to substitute stamped sheet reflectors for plastic reflectors whose surface

  The optical system is produced by vacuum metallization, in particular by alumina.

  swimming. The essential problem lies in the fact that the plastics which are most suitable for the molding of a reflector shape, followed by the production of an optical surface by metallization, generally have a poor resistance to the temperatures which are the operating temperatures of a car projector

  having the usual dimensions and power.

  In other words, the tests of implementation of construc-

  large reflectors for motor vehicle headlamps have shown that overheating

  of the headlamp are incompatible with the permanence of an indi-

  dull (metallized surface) rigorously defined optically

  (usually parabolic surface).

  To remedy this drawback, it has so far been proposed

  solutions, among which may be mentioned: the use of plastics having a good resistance to heat; such plastics exist, but their

  cost price makes them prohibitive for the construction of projec-

  tors; - the use of cheap plastic materials, incorporating reinforcements to stiffen the reflector; - production of reflectors having a non-uniform thickness, and in particular comprising thinned areas tending to limit the

  deformations due to heating up the non-useful areas of the reflector.

  None of these solutions proved to be fully satisfactory.

health.

  The present invention relates to a novel structure of

  flector, making it possible to obtain, by simple molding plastic materials

  most widely available, a reflector structure eliminates

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  the effects of deformation due to overheating

  is lying. According to the invention, the reflector is given by construction

  made of plastic in its upper region of greater

  an inner surface shape at ambient temperature substantially deviating from the desired optical form, but such that, in

  the warm-up conditions corresponding to the operation of the

  jector, the deformations of the reflector bring its internal surface to

the desired optical form.

  In other words, the internal shape of the "cold" reflector is a

  imperfect form whereas this form, after deformation due to

  temperature, becomes the ideal optical form to cooperate with the light source associated with the reflector to obtain a

light beam determined.

  In a preferred embodiment, the reflector is

  type having, throughout its width, a parabolic surface of

  evolution, closed in the lower part and in the upper part by two substantially flat cheeks, the opening contour of the reflector being defined

  by a raised edge or stiffening rib.

  For this type of reflector, the invention provides a slight reduction

  beating up and down a selected area of the parabolic surface, around a folding hinge which is preferably constituted

  by the section of the parabolic surface by a horizontal plane.

  The folded area is in all cases adjacent to the cheek -

  higher. Its total width may be between a fraction

  the total width of the reflector. Its total height can be between one-tenth and three-quarters of the half-height of the reflector. Its folding around the aforementioned hinge is

  between 0.2 and 6% (values in radians).

  The rigorous choice of folding dimensions and angles

  depends on the precise characteristics of the reflector, its

  its thickness, the characteristics of the light source

  with whom it must cooperate, of the plastic material which constitutes

  kill. This choice is in all cases within the reach of the home of art

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  who can determine it both with the help of theoretical considerations

and empirical tests.

  In particular, one can empirically

  of a mold, obtain a series of reflectors with

  progressively increasing, both for their size and for their

  drawdown, which helps to determine the optimal solution.

  In another embodiment, the reflector is provided with a series of folded zones arranged in a stepped manner. A small zone very folded is thus within a less folded average zone, itself even within a large area, even less folded, all areas being, as previously, adjacent to the upper cheek of the reflector .

  The complement of the following description with reference

  In the accompanying drawings, it will be better understood how the invention can be realized. In the accompanying drawings: FIG. 1 is a front perspective view of a parabolic mirror of rectangular opening contour, in a first embodiment of the invention; FIG. 2 is a vertical axial section of this same mirror

  reflector along the line of section II-II of Figure 1, or according to all

  the other parallel central vertical cross section;

  FIG. 3 represents a second embodiment of the invention.

  vention, in a perspective view similar to that of Figure 1.

  The reflector of FIGS. 1 and 2 is a rectangular contour reflector with an active parabolic optical surface. It is made of molded plastic and more specifically of PBT (polyterephthalate)

  butylene). Its thickness is uniformly 2 mu. This reflector com

  carries a parabolic surface P of axis 00 extending over its entire width, and at the top and bottom, cheeks J1 and J2, substantially

  planar. Part P has an optical role, by constituting the reflective surface

  of the reflector, while the cheeks Ji and J2 have only one role

  link mechanics without optical effect; a rim R delimits the con-

  opening of the reflector forming a riser or stiffening rib

  fication. The parabolic surface P has a focal length of 26.5 mm, an opening width of 190 mm and a height of 120 mm. In use, an ice (not shown) closes the reflector on its front face, and a lamp (not shown) is mounted on its rear opening S. With such a reflector structure, the commissioning of the

  projector with the planned lamp (type CRE or H4) causes heating

  considerable factors: the point B of the upper cheek JI has a temperature of the order of 106 C, while the point A at the extreme limit of the part P has a temperature of the order of 100 C, and that the central zone C of the parabola P has a temperature of the order of 80 C

(see Figure 2).

  According to the invention, and to enable the reflector to accom-

  temperature variations between the cold state and the state of

  In the manufacturing process, the quadrangular upper zone is

  Z1 of the P zone a shape folded about 2% around a

tilting hinge zl-zl.

  The folding hinge zl-zl is constituted by the sec-

  parabolic P by a horizontal plane. Zone Z1 extends

  than on the upper cheek J1, its height being one tenth of the height of the parabola P, that is to say 12ram, and its width being about

  two thirds of the width of the parabola P, that is to say about 130rmn.

  Zone Z1 is centered with respect to the vertical plane passing through the axis

  optical 0-0. When talking about a drawdown of 2% around the char-

  In other words, all sections of the parabola P with section planes such as II-II (Fig. 2) or parallel vertical planes are reduced by 2%, as shown in Fig.

  2, around their intersection with the zl-zl hinge.

  FIG. 2 shows in solid lines the shape

  real, after folding, and in dotted lines the rigorous form

  parabolic (fonrme without drawdown).

  With such an arrangement, it is found that the putting into service of the reflector, that is to say its cooperation with a suitable lamp, and the subsequent heating, result in a tilting towards the

  top of the upper cheek J1 and the folded zone Z1. After this

  the inner surface of zone Z1 is exactly

  coincidence with a parabolic surface of O-O axis revolution,

  thus producing Z1 zone, an inverse effect of the

building beat.

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  Of course, the example above is only illustrative and

  other embodiments are possible.

  Zone Z1 may be limited to the central part of the reflection

  as shown in Figures 1 and 2. It may also extend

  the entire width of the upper part of the reflec-

  below the upper cheek Ji.

  FIG. 3 represents a second embodiment of the invention.

  vention, very close to the first. In this figure, the unchanging elements

  have been designated by the same references as in Figure 1

  According to the characteristic of this embodiment, the reflec-

  tor has three folded zones Z1, Z2 and Z3 arranged in stepped tiers, Z2 being inside Zi, and Z2 inside Z3,

  three zones being, as before, adjacent to the cheek Ji.

  Figure 3 is to scale, in that the cheeks have the dimensions and relative positions shown therein. Zone ZI is, as before, folded by 2% around a horizontal hinge zl-zl. Similarly, zone Z2 is folded, but only 1% around a horizontal hinge z2-z2, and zone Z3

  is folded by 0.5% around a z3-z3 horizontal hinge.

  When such a reflector is in use, because of the heating

  three zones Zl, Z2 and Z3 have leu = internal aluminized surfaces5 which return to a parabolic form of revolution around

the O-O axis.

  It is essential to note that the drawdown of

  The temperature of at least one zone of the reflector according to the invention has nothing to do with the recesses and irregularities which, in the prior art, certain reflectors

  to modify the optical properties of the reflected light beam.

  Indeed, in such an earlier technique, the shapes of all the zones of the reflectors are considered to be invariable, and it is thus supposed that the light beam remains the same as the projector is

  "cold" or "hot". On the contrary, the essential idea of presenting

  the invention is to use extensively the plastics

  mically deformable, in relatively low thicknesses, and

  do not try to thwart the deformation during the rise in temperature.

  erature, but to compensate it a priori by optical forms

  away from the optical form needed in service.

  It will also be noted that such a solution has never been envisaged in the technique of plastic reflectors for headlights of autcmobile vehicles, although this technique is

already very old.

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FVEMNJDICiTIONS

  ]. A plastic reflector for a vehicle headlamp

  automobile, designed to cooperate with a light source for obtaining a determined reflected light beam, characterized in that it comprises by construction, at least in its upper region of greater heating, a shape of internal surface s' deviating substantially from the optically necessary form for this purpose, but

  which, in the warm-up conditions corresponding to the functioning

  the projector is deformed due to dilatation

  thermal conditions so that said inner surface returns to the optical surface.

  necessary for the production of the specified beam.

  2. A reflector according to claim 1, characterized in that

  that it coaporte, at least in the upper part of larger

  at least one zone folded around a hinge.

  3. A reflector according to claim 2, of the rectangular opening type having a central parabolic surface, and two upper and lower cheeks, characterized in that it comprises at least one quadrangular zone folded from bottom to top around a

  substantially horizontal hinge, this folded area being adjacent

te to said upper cheek.

  4. A reflector according to claim 3, characterized in that said quadrangular zone extends over a height between

  the tenth and three-fourths of the half height of the para-

  bolique, and over-a width of between one tenth of the width of

  the parabolic surface, its drawdown being between 0.2 and 6%.

  5. A reflector according to one of claims 3 and 4, characterized

  it has several folded zones.