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(11) | EP 1 589 282 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Thin-plate light for motor vehicles |
| (57) A lighting system, in particular for motor vehicle lights, is made up of one or more
cells, each comprising: a transparent dielectric module in the form of a plate (2),
with two opposite main faces (I, II); a substantially point-like source (1) set in
the proximity of a first (I) of the two main faces of said module; a primary reflector
(3) formed on the second (II) of the main faces of the module for reflecting a first
time the light coming from the source (1) that has traversed the plate (2); and a
secondary reflector (4) formed on the first main face (I) of said module, for reflecting
a second time the light already reflected by the primary reflector and directing it
towards the outside of the module, on the side of said second main face (II), so as
to collimate it in a pre-determined direction. The primary reflector (3) is made up
of two parts: a substantially curved central section (A), coated with a reflecting
layer (5) which is designed for reflecting a portion of the rays emitted by the source
(1); and a substantially plane and transparent peripheral section (B), which is designed
for reflecting in total internal reflection (TIR) another portion of the rays emitted
by the source (1). The secondary reflector is made up of two sections: a first section
(C), which is coated with a reflecting layer and is designed for receiving the light
reflected by said central section (A) of said primary reflector and reflecting it
towards the transparent section (B) of the primary reflector; and a second section
(D), which is coated with a reflecting layer and is designed for receiving the light
reflected in TIR from the transparent section B and reflecting it again outwards,
through said section B of said primary reflector. |
BACKGROUND OF THE INVENTION
Field of the invention
[0001] The present invention relates to the field of lighting systems, and in particular lights for motor vehicles, of the type comprising one or more elementary cells, each including: a transparent dielectric module in the form of a plate, with two opposite main faces; a substantially point-like source set in the proximity of a first one of the two main faces of said module; a primary reflector formed on the second of the main faces of the module for reflecting a first time the light coming from the source that has traversed the plate; and a secondary reflector formed on the first main face of said module, for reflecting a second time the light already reflected by the primary reflector and directing it towards the outside of the module, on the side of said second main face, so as to collimate it in a pre-determined direction.
Prior art
[0002] A lighting system of the type specified above has already been proposed by the present applicant in the European patent No. EP 0 766 115 B1 and in the corresponding U.S. patent No. US 5 841 596, as likewise in the European patent No. EP 0 767 393 B1 and in the corresponding U.S. patent No. US 5 884 995. In said system, illustrated in Figure 1 of the annexed plate of drawings, the individual collimation cell operates in a mode similar to a telescope of the Cassegrain type. With reference to Figure 1, a point-like light source 1 is located in the proximity of a first face I of a transparent plate 2 made of plastic material. The light emitted by the source 1 is coupled within the plate 2 through a transparent portion of said face I, impinges upon a primary reflector 3 set on the second face II of the transparent portion and generally obtained by coating a portion of said face II with a reflecting layer, and is reflected by said primary reflector 3 towards a secondary reflector 4 set on the face I about said transparent portion and generally obtained by coating a portion of said face I with a reflecting layer. The light is again reflected by the secondary reflector 4 towards the face II and exits from the plate through a transparent portion of said face II, undergoing a refraction. The primary reflector 3 and secondary reflector 4 have shapes which are designed for producing in combination a collimation of the beam emitted by the point-like source 1. The point-like source 1 can be located in a position corresponding to the transparent portion of the face 1 and possibly englobed in the plate in a position corresponding to said transparent portion.
[0003] In the above known solution, only one portion of the rays emitted by the source (which typically has a lambertian emission lobe) is collected by the primary reflector, where a significant portion of said rays is collected by the transparent portion of the face II, through which the rays exit from the plate.
PURPOSE OF THE INVENTION
[0004] The purpose of the present invention is to improve the performance of the optical system proposed previously by increasing control of the light distribution and hence the value of intensity in a pre-determined direction.
THE INVENTION
[0005] According to the present invention, the aforesaid purpose is achieved by the fact that:
- said primary reflector is made up of two parts: a central section A, which is substantially curved and is coated with a reflecting layer, which is designed for reflecting a portion of the rays emitted by the source; and a substantially plane and transparent peripheral section B, which is designed to reflect in total internal reflection (TIR) another portion of the rays emitted by the source; and
- said secondary reflector is made up of two sections: a first section C, which is coated with a reflecting layer and is designed for receiving the light reflected by said section A of said primary reflector and reflecting it towards said transparent section B of said primary reflector; and a second section D, which is coated with a reflecting layer and is designed to receive the light reflected in TIR by said transparent section B and reflect it towards said section B of said primary reflector.
[0006] In the system according to the invention, the following two solutions are consequently combined together:
1) the primary reflector A subtends an angle, with respect to the source, so that the rays emitted by the source at larger angles are reflected by the transparent portion B of the face II as a result of TIR; and
2) the secondary reflector consists of two portions: a portion C, which operates prevalently on the rays reflected by the primary reflector A; and a portion D, which operates prevalently on the rays reflected by TIR by the transparent portion B of the face II.
[0007] In a preferred embodiment, the primary reflector A is radiused to the transparent portion B with a continuous profile and with a continuous curvature, so that the portions C and D of the secondary reflector operate in a substantially exclusive way on the rays reflected by the primary reflector A and by the transparent portion B of the face II, respectively.
[0008] Thanks to said solution, it is possible to design the reflector C so as to collimate the rays coming from the reflector A, and the reflector D so as to collimate the rays coming from the transparent portion B, thus maximizing control of the distribution. A superimposition, even a partial one, of the rays (reflected by the primary reflector) on the secondary reflector would not enable optimization of the secondary reflector in said region of superimposition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The characteristics and advantages of the present invention will emerge clearly evident in the course of the ensuing detailed description, which is provided purely by way of non-limiting example, with reference to the attached plate of drawings, in which:
- Figure 1 is a cross-sectional view of a cell of the light according to the known art;
- Figure 2 is a cross-sectional view of a cell of the light according to a first embodiment of the invention, with rotational symmetry, which is designed to be installed on a motor vehicle so as to have the axis of revolution of the reflector parallel to the longitudinal axis of the vehicle;
- Figure 3 is a cross-sectional view of a cell of the light according to a second embodiment of the invention, which does not present rotational symmetry, and which is designed to be installed on a motor vehicle so as to have the axis of revolution of the reflector inclined by an angle β with respect to the longitudinal axis of the vehicle;
- Figure 4 is a perspective view of a light according to the invention, designed to be installed on a motor vehicle with the axis of the reflector not coinciding with the longitudinal axis of the vehicle;
- Figures 5A, 5B, and 5C illustrate a cell of the light according to three variants of the invention in the case where the primary reflector is of a parabolic type (Figure 5A), of an elliptical type (Figure 5B), and not with rotational symmetry (Figure 5C);
- Figure 6 illustrates a cell of the light according to a further variant of the invention, in which the secondary reflector deviates the rays by a pre-determined angle, and a transparent portion is provided that is equipped with micro-optical systems for creating the required photometric pattern;
- Figure 7 illustrates a cell of the light according to a further embodiment, with a hexagonal shape, in which the primary reflector A has not been illustrated in order to highlight the secondary reflector made up of the parts C and D, the chip-LED source being set at the centre of the cell;
- Figure 8 illustrates a simulation of the distribution of the light intensity obtained with a non-sequential ray-tracing software, which shows control of the light distribution achieved for an angle β of 45°; and
- Figure 9 is a perspective view of a light according to the invention made up of a plurality of hexagonal cells.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Figure 2 is a cross-sectional view of a first embodiment of the collimator according to the present invention, in a plane of cross section perpendicular to the plate. The parts corresponding to those of Figure 1 are designated by the same reference numbers. Thus, the point-like light source (typically a chip-LED) is designated by 1. The plate, made of synthetic material, is designated by 2, and I and II designate the two main faces of the plate 2 on which the primary reflector 3 and the secondary reflector 4 are formed. As illustrated above, the primary reflector 3 has a central section A, which is reflecting in so far as it is equipped with a reflecting coating 5, and a peripheral section B, which does not have a reflecting coating, but gives rise to a total internal reflection (TIR) of the rays of light coming from inside the plate with an angle of inclination with respect to the vertical direction of the figure greater than a given value.
[0012] Consequently, all the rays R1 coming from the source 1 that impinge upon the central section A of the primary reflector are reflected by the latter on the section C (which is a central annular area of the face I) of the secondary reflector, which in turn reflects them outwards in a direction substantially perpendicular to the section B, so that the latter allows them to pass outwards. All of the rays R2 coming from the source 1 that impinge directly upon the peripheral section B of the primary reflector are reflected by this by TIR on the peripheral section D of the secondary reflector, which then reflects them outwards, again in a direction substantially perpendicular to the section B, so that the latter allows them to pass outwards.
[0013] In the example illustrated in Figure 2, the profile of the right-hand part (with reference to the figure) of the section A of the primary reflector is a profile of parabola with focus in a point corresponding to the source and axis AX inclined by an angle α with respect to the vertical. The left-hand part of the section A has likewise an axis passing through the source and set in a way specularly symmetrical with respect to the axis AX. Consequently, said section A collimates the rays emitted by the source with an angle α on the secondary reflector C.
[0014] The size of the primary reflector A is such as to subtend an angle with respect to the source again equal to α, so that the point of radiusing between the sections A and B is continuous both in profile and in curvature. The angle α is chosen so as to be greater than the TIR angle so as to guarantee conditions of TIR on the entire section B of the face II. The choice of an angle slightly greater than the TIR angle enables minimization of the size of the primary reflector A.
[0015] As already mentioned, the rays reflected by the primary reflector A are subsequently reflected by the secondary reflector C. The rays reflected by the transparent portion B are instead reflected by the secondary reflector D. In the configuration of Figure 2, the light is installed on a motor vehicle so that the axis z perpendicular to the surface of the cell is substantially parallel to the longitudinal axis of the vehicle.
[0016] The primary reflector A generates an annular image of the point-like source. Said image can be: at infinity, in the case of section A being parabolic; virtual, in the case of section A being hyperbolic; or real, in the case of section A being elliptical. The transparent reflecting portion B generates, instead, a virtual point-like image of the chip-LED.
[0017] The secondary reflector C is a complex surface that operates on the rays reflected by the primary reflector A in order to generate a desired distribution of light. The secondary reflector D operates, instead, on the rays reflected by the transparent reflector B to generate a desired distribution of light. Each of the two surfaces C and D can be segmented into a number of sectors so as to have an envelope in common (and continuous in the point of radiusing).
[0018] As very frequently occurs, the light cannot be positioned perpendicular to the longitudinal axis of the vehicle, but rather inclined with respect to two angles: the first is formed by rotating the light with respect to the axis Y (which exits from the plane of the figure); the second is formed by rotating it with respect to the axis X (see Figure 4).
[0019] These two rotations are equivalent, on account of the design of the optical surfaces, to just one rotation. In fact, we shall introduce a unit vector p that defines the direction of the longitudinal axis of the vehicle. We shall define, then, a new system of cartesian co-ordinates X', Y', Z', in which Z' = Z and the axis X' coincides with the projection of the unit vector p on the external surface of the light. In the system X', Y', Z', the two rotations defined above are equivalent to just one rotation with respect to the axis Y', with an angle comprised between the unit vector p and the plane X',Y'.
[0020] For this reason, on account of the design of the reflecting surfaces, it is sufficient to consider just one angle of rotation with respect to the axis Y designated, in Figure 3, by β. Figure 3 shows precisely a cell of the light according to the invention, designed for being installed so as to have the axis of the reflector oriented by the angle β with respect to the longitudinal axis of the motor vehicle.
[0021] The primary reflector A is constituted by a surface of an elliptical, parabolic or hyperbolic type. Figure 3 represents the case of a parabolic type (similar to Figure 2), in which the axis of rotation of the parabola has an angle α with respect to the straight line perpendicular to the faces of the cell.
[0022] The choice of the type of surface of the primary reflector A is dictated by the angle β, by the thickness of the device, and by considerations regarding the luminance of the cell.
[0023] Figure 5A illustrates a case where the surface of the primary is of a parabolic type, and the angle of collimation β is such that a part of the light reflected by the secondary reflector C arrives again on the primary reflector (in the portion designated by 4); this entails a loss of efficiency of the device or, in any case, a loss of control of part of the light. In order to prevent this effect, it is possible to resort, in the case of Figure 5A, to a different shape of the primary reflector. Figure 5B illustrates a type of primary reflector A of elliptical cross section with one focus in the source and the other focus determined with the following methodology: considering the left-hand side of the profile of the cell of Figure 5B, the focus 2 is determined as the intersection of the two extreme rays 1 and 4 reflected by the primary reflector A. The point 1 is the point of intersection between the primary reflector A and the transparent section B, the TIR angle determines the ray reflected by the point 1 of the primary reflector. The ray reflected by the point 4 is chosen so that the ray reflected by the secondary reflector C will exit from the cell with an angle β passing through the point 1, preventing it from arriving back, as occurred in the case of Figure 5A on the primary reflector A. Considering the right-hand side of the profile of the cell of Figure 5B, it is noted that the focus 2 of the primary reflector A determines an area 3 of the transparent section B from which rays do not exit. Said area 3 will present as an area of shadow, if the observer is positioned in the direction given by the angle β. The configuration of Figure B enables efficiency/control of the light emitted by the device not to be lost, but leads to an extension of the area of shadow represented by the primary reflector A.
[0024] In order to overcome both of the drawbacks, loss of efficiency/control and lack of uniformity of luminance, the primary reflector A can be built not having rotational symmetry as indicated in Figure 5C. The cross section of Figure 5C illustrates a surface having a cross section of an elliptical type in the left-hand area of the profile of the cell and of a parabolic type in the right-hand area.
[0025] The secondary reflector, in this example of light, is not a surface of rotation. The part of reflector C deflects the rays coming from the primary reflector A so that, after the interface B, they will exit with a preferential angle β to form the desired distribution of intensity. The part of reflector D receives the rays that impinge upon the interface B with an angle greater than the limit angle (TIR) and deflects them according to the same principle as that of the reflector C.
[0026] The part of transparent surface B may be smooth, in which case the distribution of intensity is created by the reflecting surfaces C and D; there may be provided an additional transparent portion, on the internal surface of which there are present microlenses or prisms calculated so as to widen the distribution of light. Figure 6 is an example of configuration in which the array of microlenses is inserted in the internal part of a transparent portion set in front of the individual elementary cells. Said transparent portion bearing the microlenses may be colourless or else coloured.
[0027] Also the dielectric plate which is designed for collimating the light emitted by the sources can be coloured; in both cases, the colour of the transparent portion must be such as to transmit all or almost all of the light of the wavelength emitted by the corresponding microsource or microsources.
[0028] The individual elementary cells which make up the light may have any geometrical shape (circular, rectangular, hexagonal, etc.), said shape being dictated, principally, by stylistic reasons. Figure 7 is a front view of a hexagonal elementary cell. The chip-LED source is positioned in the centre and is visible in so far as the primary reflector A has been masked in order to highlight the absence of rotational symmetry of the secondary reflectors C and D.
[0029] On the elementary cell of Figure 7, which is optimized to present an angle β of 45°, simulations have been made, obtained with non-sequential ray-tracing software. Figure 8 represents the distribution of intensity in which the excellent degree of control of the outgoing beam is highlighted. The value of efficiency of the device is equal to 70%, with a value of reflectance of the reflecting surfaces of 0.85.
[0030] For the purposes of the present invention, the number of sources for each individual cell that forms part of the light does not emerge as a constraint. It is in fact possible to set alongside one another a number of microsources about the axis of the individual elementary cell in order to increase the flow of light.
[0031] The arrangement of the individual cells for the composition of the light can be obtained in various ways, dictated by requirements of a stylistic nature and of encumbrance that the light must satisfy. Figure 9 illustrates, by way of example, a case in which a multitude of cells with a hexagonal shape have been set alongside one another.
1. A lighting system, in particular a motor-vehicle light, made up of at least one elementary
cell, each cell including: a transparent dielectric module in the form of a plate
(2), with two opposite main faces (I, II); a substantially point-like source (1) set
in the proximity of a first (I) of the two main faces of said module; a primary reflector
(3) formed on the second (II) of the main faces of the module for reflecting a first
time light coming from the source (1) that has traversed the plate (2); and a secondary
reflector (4) formed on the first main face (I) of said module, for reflecting a second
time the light already reflected by the primary reflector and directing it towards
the outside of the module, on the side of said second main face (II), so as to collimate
it in a pre-determined direction,
said lighting system being characterized in that:
said lighting system being characterized in that:
- said primary reflector (3) is made up of two parts: a substantially curved central section (A), coated with a reflecting layer (5) which is designed to reflect a portion of the rays emitted by the source (1); and a substantially plane and transparent peripheral section (B), which is designed to reflect in total internal reflection (TIR) another portion of the rays emitted by the source (1); and
- said secondary reflector is made up of two sections: a first section (C), which is coated with a reflecting layer and is designed for receiving the light reflected by said central section (A) of said primary reflector and reflecting it towards said transparent section (B) of said primary reflector; and a second section (D), which is coated with a reflecting layer and is designed for receiving the light reflected in TIR by said transparent section B and reflecting it again outwards through said section B.
2. The device according to Claim 0, characterized in that said reflecting layers on the surfaces A, C and D are metal coatings.
3. The device according to Claim 0, characterized in that said reflecting layers on the surfaces A, C and D are multilayer dielectric coatings.
4. The device according to Claim 0, characterized in that said reflecting layer on the surface A is partially transparent so as to transmit
a portion of the light emitted by the source and incident on said primary reflector
A.
5. The device according to Claim 0, characterized in that said primary reflector A is constituted by a surface obtained through the revolution
of at least one segment of conical curve (understood as line resulting from the intersection
of a cone with a plane) about an axis passing through the source and perpendicular
to the main faces of the plate.
6. The device according to Claim 0, characterized in that the source is positioned in the proximity of the focus of said conical curve.
7. The device according to Claim 0, characterized in that said segment of conical curve is a segment of parabola having axis inclined towards
the outside by an angle greater than or equal to the TIR angle.
8. The device according to Claim 0, characterized in that said segment of conical curve is a segment of ellipse having the first focus in the
proximity of the source.
9. The device according to Claim 0, characterized in that said primary reflector A is constituted by a surface not of revolution.
10. The device according to Claim 0, characterized in that said section A of the primary reflector and said section B of the primary reflector
are radiused together so that both the profile and the curvature are continuous in
the locus of the points of radiusing.
11. The device according to Claim 0, characterized in that said secondary reflector C is constituted by a multiplicity of segments of quadric
surfaces, for example paraboloids, ellipsoids or hyperboloids, radiused together in
a discontinuous way.
12. The device according to Claim 0, characterized in that said secondary reflector C is constituted by a multiplicity of segments of asymmetrical
cones, which are designed for collimating the light coming from the annular image
of the source, said image being generated by said surface of revolution of the primary
reflector A, in a pre-determined direction.
13. The device according to Claim 0, characterized in that said secondary reflector D is constituted by a multiplicity of segments of quadric
surfaces, for example paraboloids, ellipsoids or hyperboloids, radiused together in
a discontinuous way.
14. The device according to Claim 0, characterized in that said quadric surfaces are paraboloids of rotation having their focus in the virtual
image of the source, said image being generated by the transparent section B of said
primary reflector.
15. The device according to Claim 0, characterized in that said paraboloids of rotation have axes mutually parallel so as to collimate the light
in a pre-determined direction.
16. The device according to Claim 0, characterized in that said paraboloids of rotation have axes that are not mutually parallel, oriented so
as to form a pre-determined distribution of light.
17. The device according to any one of the preceding claims, characterized in that said transparent plate is colourless.
18. The device according to any one of the preceding claims, characterized in that said transparent plate is coloured and in that colouring of each elementary cell is such as not to absorb the light emitted by the
source in said cell.
19. The device according to any one of the preceding claims, characterized in that in at least one of said cells is present more than one source, said sources being
positioned close to one another.
20. The device according to any one of the preceding claims, characterized in that said source is a LED in the form of a chip, i.e., without the package.
21. The device according to Claim 0, characterized in that said chip is englobed in the plate.
22. The device according to any one of the preceding claims, characterized in that the thickness of the plate is less than 15 mm.
23. The device according to any 'one of the preceding claims, characterized in that a second transparent portion is provided in a position corresponding to the beam
coming out of said plate.
24. The device according to Claim 0, characterized in that said transparent portion is coloured, whilst the dielectric constituting said plate
is colourless.
25. The device according to Claim 0, characterized in that said transparent portion has, on its internal surface facing said plate, a multiplicity
of microlenses and/or prisms which are designed for conforming/deflecting the light
beam coming out of said plate.
26. A light for a vehicle, in particular a back light, characterized in that it comprises a device according to any one of the preceding claims.
27. A headlight for a vehicle, characterized in that it comprises a device according to any one of Claims 1 to 25.