FR2796347A1 - Automobile rear view mirror comprises casing part inside and part outside vehicle having reflecting mirror and input and output lenses with diffractive surface displacing rays laterally - Google Patents

Abstract

The rear view mirror comprises casing (1) which has part (1a) emerging inside the vehicle and part (1b) emerging outside the vehicle as well as reflecting mirror (2) in the bottom of casing. It comprises input convergent lens (13a) and output divergent lens (13b) in the inside and outside parts respectively. These lenses have diffractive surface which ensures lateral displacement of the rays.

Description

 The present invention relates to rear view mirrors for a motor vehicle and in particular to side mirrors. BACKGROUND OF THE INVENTION

Usually, a side mirror is constituted by a mirror disposed in a housing which is outside the vehicle.

Such mirrors have many disadvantages.

 Since they protrude outside the vehicle, they can be a source of collisions.

In addition, they also pose a reliability problem since they can be easily damaged or broken.

In addition, they cause a significant additional aerodynamic drag.

 Also, they pose security problems, since they force the driver to momentarily leave the road eyes to take notice of the image they reflect.

Finally, the images reflected by such mirrors may not be totally satisfactory given the constant pollution to which these mirrors are subjected and also given the fact that the image they send back is seen through the windows of the window. vehicle.

To overcome these disadvantages, it has already been proposed mirrors which, as shown in Figure 1, comprise a housing 1 which comprises a portion 1 opening out of the vehicle and a portion 1b opening to the inside thereof, and a mirror 2 disposed in the bottom of the housing 1.

It also comprises convergence and divergence optics 3a and 3b arranged at the input and at the output of the housing for shaping the light beams passing therethrough, as well as deflection prisms 4a and 4b disposed between the mirror 2 and the optics 3a and 3b .

Such convergence and divergence optical structures 3a and 3b, as well as deviating prisms, make it possible to provide the mirror function in a reduced volume.

However, they are expensive and a complex assembly. The invention proposes a rear view mirror for a motor vehicle of the type comprising a housing which has a portion which opens into the vehicle interior and a portion which opens out of the vehicle, and an optical element of reflection disposed in the bottom of said housing and at least one optical element for shaping the light rays passing through the housing, characterized in that it comprises at least one optical element with a diffractive grating.

The invention is advantageously completed by the following different characteristics, taken alone or in all their technically possible combinations - a diffractive grating optical element is a convergence or divergence optics and a deflection function; it comprises two optics, one of convergence, the other of divergence, respectively arranged in one and the other of the two parts of the housing, each of these two optics being a diffractive grating optics; a convergence or divergence optic has a plane face and a curved face and a diffractive grating is etched on its plane face; the diffractive grating is of a configuration such that it provides achromatization in at least one band of wavelength in the visible range, typically between 0.45 μm and 0.7 μm; the network is a binary network with 2 "phase levels where n is an integer, the networks of one and the other of the two convergence / divergence optics are identical.

Other features and advantages of the invention will become apparent from the description which follows. This description is purely illustrative and not limiting. It should be read with reference to the accompanying drawings in which - Figure 1 is a schematic sectional representation of a rear view mirror housing having a portion opening into the vehicle interior and a portion opening outwardly thereof conforming one embodiment of the state of the art; FIG. 2 is a schematic representation of a rearview mirror according to a possible embodiment of the invention; FIGS. 3a and 3b illustrate two possible profiles for the diffractive gratings of a rearview mirror according to the invention.

The rear-view mirror illustrated in FIG. 2 comprises, in the same way as that of FIG. 1, a housing 1 which comprises a portion 1a opening into the interior of the vehicle and a portion 1b opening outwardly therefrom, and a deflection mirror 2 disposed in the bottom of the housing 1.

It comprises optical input components and outputs 13a and 13b which are a convergence lens and a divergence lens respectively arranged in the part 1a and in the part <B> lb, </ B> in the vicinity of the ends of them.

These lenses have the particularity to present one and the other a diffractive surface, which in addition to a function of convergence or divergence, ensures in particular the lateral deviation of the beams.

Thus, the optical groups that constitute, in the devices of the state of the art illustrated in Figure 1, the elements 3a and 4a on the one hand and the elements 3b and 4b on the other hand are each replaced by a single component hybrid 13a, 13b, having both diffractive and refractive properties.

This component provides several functions: optical power, beam deflection, achromatization on the visible band to avoid iridescence phenomena (typically achromatization between 0.45 pm and 0.7 Nm), etc.

The diffractive components 13a, 13b each have a planar face and a curved face.

The flat face of a diffractive component 13a, 13b is the surface on which a diffractive grating is etched. The shape of the curved face can be convex, concave, complex, and so on. and depends on the network etched on the plane face and the functions that one wishes to see performed by the component. In the case where the diffractive grating only serves to ensure the deflection of the beam, it is constituted by a rectilinear plane array.

Alternatively, it may also be constituted by a circular network, by a combination of circular networks or straight networks or by networks of complex shapes.

Diffractive networks can be of any type. They are, for example, binary networks with 2, 4, 8 or 16 phase levels (and, more generally, at 2 "level, where n is an integer), depending on the desired performances (in particular on the diffraction efficiency, that is to say percentage of luminous flux received which is used to create the image) and the technological feasibility (and in particular according to the optical material used, glass or plastic).

For example, in the case of a network with four phase levels, the pitch of the network is of the order of 25 μm (with variations on the surface) for a total dimension of the network of approximately 80 × 80 mm.

An example of a four-step stepped binary profile is shown in Figure 3a.

Such a network is made by chemical etching with two masks. Other types of etching than binary engravings can be envisaged.

In particular, in the case of optical components 13a, 13b made of an optical plastic material, other types of etchings can be made by stamping and in particular, as illustrated in FIG. 3b, with sloping diffractive profiles, allowing improvement of diffraction efficiency and decrease of parasitic light.

Furthermore, the gratings engraved on the components 13a and 13b are advantageously the same, which minimizes the tools for producing the etching masks.

For this purpose, a single lens (not shown in the figures) is then inserted in the optical path, which provides a desired magnification, of the order of 2. Other embodiments of the invention than that which has just been to be described are conceivable.

In particular, it can be envisaged that only one of the two components 13a, 13b carries a diffractive grating.

Claims (7)

<U> CLAIMS </ U> 1. Rearview mirror for a motor vehicle of the type comprising a housing which has a portion which opens into the vehicle interior and a portion which opens out of the vehicle, and an optical reflection element disposed in the bottom of said housing and at least one optical element for shaping the light rays passing through the housing, characterized in that it comprises at least one optical element with a diffractive grating. 2. Mirror according to claim 1, characterized in that a diffractive grating optical element is a convergence optics or divergence and a deflection function. 3. Mirror according to claim 2, characterized in that it comprises two optical converging one, the other of divergence, respectively arranged in one and the other of the two parts of the housing, each of these two optical being a diffractive grating optics. 4. Mirror according to one of claims 2 and 3, characterized in that convergence or divergence optics has a flat face and a curved face and in that a diffractive grating is etched on its flat face. 5. Mirror according to one of the preceding claims, characterized in that the diffractive grating is of a configuration such that it provides an achromatization in at least one band of wavelength in the visible range, typically between 0.45 Nm and 0.7 Nm. 6. Mirror according to one of the preceding claims, characterized in that the network is a binary network with 2 "phase levels where n is an integer. 7. Rearview mirror according to claim 3, characterized in that the networks of one and the other of the two convergence / divergence optics are identical.