Lighting device provided with an array of microlenses

Abstract

The invention relates to a lighting device (1) for a motor vehicle, the lighting device comprising: - a light source (2); - an array of microlenses (3); and - a collector (4) configured to project an image of the light source onto an entrance face (31) of the array of microlenses, the collector comprising: - an elliptical first reflecting surface (41), the first reflecting surface comprising a first focal zone (Z1) and a second focal zone (Z2); and - a parabolic second reflecting surface (42), the second reflecting surface comprising a single focal zone (ZC), the light source being positioned at the first focal zone of the first reflecting surface, the single focal zone of the second reflecting surface being positioned at the second focal zone of the first reflecting surface.

Description

Light-emitting device equipped with a microlens array Technical field of the invention

[0001] The invention relates to a lighting device for a motor vehicle, the lighting device comprising a microlens array. In particular, the invention relates to a lighting device intended to produce a low-beam headlight beam. Prior art

[0002] Motor vehicles equipped with a lighting system consisting of a microlens array are known. Figure 1 schematically illustrates a lighting system 1' according to the prior art. The lighting system 1' comprises a light source 2', a microlens array 3', and a collector 4' configured to project an image of the light source 2' onto an entrance face of the microlens array 3'.

[0003] The microlens array 3', commonly referred to by its English term "micro lens array" or its abbreviation "MLA", is an afocal optical component comprising a network of juxtaposed microlenses. The microlens array extends perpendicularly to an illumination axis X' of the light source. Each microlens is designed to project an image of the light source 2'. The images projected by each microlens are superimposed to form an overall image with predefined illumination characteristics.

[0004] The collector 4' is an optical component interposed between the light source 2' and the microlens array 3'. It is designed to illuminate the microlens array with a collimated light beam to avoid a phenomenon known as coupling or "crosstalk." Coupling occurs when a light ray enters the microlens array through the entrance face of a first lens and exits the array through the exit face of a second microlens, which is different from the first. This phenomenon leads to a degradation of the image projected by the light source.

[0005] A luminous device 1' equipped with a microlens array advantageously projects a light beam with predefined shape characteristics. Such a luminous device is therefore particularly suitable for producing a low-beam headlight beam. A low-beam headlight beam includes an upper cutoff with a raised section designed to prevent glare for oncoming drivers. To effectively illuminate the road while preventing glare, the cutoff and raised section must be particularly sharp and precisely positioned.

[0006] Lighting devices with a microlens array, as known in the prior art, nevertheless have several drawbacks. To project a good quality image, microlens arrays require illumination from a light source coupled with a collector exhibiting high sharpness, a large numerical aperture, no chromatic aberration, and a long focal length. Such collectors are generally very bulky. In particular, they require significant depth along the X' illumination axis. Lighting devices with a microlens array are therefore particularly bulky along the longitudinal axis of the vehicle. Their integration into a motor vehicle is thus complex. Presentation of the invention

[0007] The object of the invention is to provide a lighting device equipped with a microlens array which at least partially remedies the above disadvantages and improves upon known lighting devices of the prior art.

[0008] More specifically, a first object of the invention is a lighting device comprising a light source, a microlens array and a collector configured to project to infinity an image of the light source which is particularly compact along the illumination axis of the lighting device.

[0009] The invention relates to a lighting device for a motor vehicle, comprising: - a light source, - a microlens array, and - a collector configured to project an image of the light source onto an input face of the microlens array, characterized in that the collector comprises: - a first elliptical reflecting surface, the first reflecting surface comprising a first focal zone and a second focal zone, and - a second parabolic reflecting surface, the second reflecting surface comprising a single focal zone, the light source being positioned at the level of the first focal zone of the first reflecting surface, the single focal zone of the second reflecting surface being positioned at the level of the second focal zone of the first reflecting surface.

[0010] The lighting device may include one or more of the following characteristics taken alone or in combination.

[0011] The first reflecting surface may include a first optical axis passing through the first focal zone and the second focal zone of the first reflecting surface. The second reflecting surface may include a second optical axis parallel to the axis of propagation of the light rays reflected by the second reflecting surface. The first optical axis may form an angle greater than or equal to 45° with the second optical axis, or even greater than or equal to 60°, or even approximately 90°.

[0012] The light source may consist of a single semiconductor electroluminescent element.

[0013] The light source may include an emitting surface of substantially square or substantially rectangular shape.

[0014] The lighting device may include a corrective lens interposed between the first and second reflecting surfaces along the path of the light rays from the light source. "Along the path" here means that the corrective lens is interposed along the path that the light rays follow between the first and second reflecting surfaces.

[0015] The corrective lens may include an entrance surface positioned between the first reflecting surface and the second focal area of ​​the first reflecting surface.

[0016] The corrective lens can be optimized to improve the sharpness of the left lateral edge and the upper edge of the image projected by the collector onto the microlens array if the lighting device is intended for use in a right-hand drive vehicle.

[0017] The lighting device may comprise a single monolithic component, in particular, obtained by plastic injection, the first reflective surface and the second reflective surface being formed on said monolithic component.

[0018] The lighting device can be configured to produce a low beam type lighting beam, the lighting beam including a cut-off provided with a raised edge. Presentation of the figures

[0019] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which:

[0020] This is a schematic view of a lighting device according to the state of the art.

[0021] This is a schematic view of a lighting device according to one embodiment of the invention.

[0022] This is a schematic and perspective view of a microlens matrix of a lighting device according to an embodiment of the invention.

[0023] Laest is a view of a projection of a beam of light produced by a lighting device according to an embodiment of the invention.

[0024] This is a first perspective view of a light source, two reflecting surfaces and a corrective lens of a lighting device according to an embodiment of the invention.

[0025] This is a second perspective view of the light source, the two reflecting surfaces and the correcting lens of the light device.

[0026] Laest is an isolux graph obtained with a collector according to an embodiment of the invention, the collector being without a corrective lens.

[0027] Laest is an isolux graph obtained with a collector according to an embodiment of the invention, the collector being equipped with a corrective lens. Detailed description

[0028] Figure 1 schematically illustrates a lighting device 1 for a motor vehicle according to an embodiment of the invention. The lighting device 1 is configured, in particular, to produce a low-beam headlight beam. The lighting device is thus intended to be integrated into the front of a vehicle, for example, to the left or right of the vehicle's grille, and to project the lighting beam forward. The lighting beam is centered on a lighting axis X. When the lighting device is in its normal mounting position on a vehicle, the lighting axis X is substantially parallel to a longitudinal axis of the vehicle, that is, substantially parallel to an axis along which the vehicle travels in a straight line. The lighting beam includes an upper cut-off provided with a raised section. The raised section is positioned substantially at the center of the upper cut-off and defines a left and a right portion of the lighting beam.Left and right are defined from the perspective of an observer facing the direction of the X-axis of illumination. When a motor vehicle is intended to be driven in a country with right-hand traffic, the left side of the headlight beam illuminates less high than the right side. Conversely, when a motor vehicle is intended to be driven in a country with left-hand traffic, the right side of the headlight beam illuminates less high than the left side.

[0029] The lighting device 1 comprises a light source 2, a microlens array 3, and a collector 4 configured to project an image of the light source onto an entrance face 31 of the microlens array. The collector 4 is therefore interposed between the light source 2 and the microlens array 3, along the direction of propagation of the light rays emanating from the light source.

[0030] The light source 2 preferably comprises a semiconductor electroluminescent element, in particular a single semiconductor electroluminescent element. The semiconductor electroluminescent element may be a light-emitting diode (LED). The semiconductor electroluminescent element may be connected to a printed circuit board in a conventional manner. The semiconductor electroluminescent element includes an emitting surface for emitting light rays when the light source is supplied with an electric current. The emitting surface has a substantially square or substantially rectangular shape. "Substantially square" or "substantially rectangular" shape includes squares or rectangles in the geometric sense of these terms, but also geometric shapes corresponding to squares or rectangles with slightly rounded corners due to manufacturing constraints of the emitting surfaces.As we will see in more detail later, it is advantageous that the emissive surface of the light surface includes at least one 90° angle as sharp as possible, that is to say with a connecting radius between two adjacent edges as small as possible.

[0031] The diagram illustrates in more detail one embodiment of the microlens array. The microlens array 3 extends in a plane oriented generally transversely to the illumination axis X, for example, perpendicularly to the illumination axis X. It may have a generally rectangular shape. It includes an entrance face 31 facing the collector 4 and an exit face 32 facing the scene intended to be illuminated by the lighting device. The microlens array 3 comprises an array of microlenses 33 arranged in a matrix pattern. The microlens array may, for example, comprise at least ten microlenses in height and at least ten microlenses in width. The surface area of ​​each microlens may be on the order of one square millimeter. The microlens array may be made of a transparent plastic material. The microlens array may be obtained by injecting a polymer into an injection mold.In particular, the first microlens matrix can be made of a polymer chosen from polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin copolymer (COC), cycloolefin polymer (COP).

[0032] Each microlens 33 is designed to project an anamorphic image of the emitting surface of the light source 2. An anamorphic image of an object is an image whose aspect ratio is altered. When the emitting surface is square or rectangular, the image projected by each microlens 33 is also a square or a rectangle, but with a potentially different aspect ratio than that of the emitting surface. As an example, three images I1, I2, and I3 projected by three distinct microlenses 331, 332, and 333 of the microlens array are shown. The first image, I1, is a small rectangle; the second, I2, is a medium rectangle; and the third, I3, is a large rectangle. The images I1, I2, and I3 are superimposed to form the illumination beam.The different images I1, I2, I3 are not necessarily centered on the X lighting axis, but on the contrary, can be advantageously offset from the X lighting axis, so as to compose distinct lighting zones.

[0033] Figure 1 illustrates an example of a projection, onto a plane perpendicular to the illumination axis X, of a light beam FE from the lighting device 1. This projection results from the superposition of multiple images of the emitting surface of the light source 2, each image originating from a separate microlens 33. In this example, each image comprises one of four square or rectangular shapes F1, F2, F3, and F4. Note that the four square or rectangular shapes F1, F2, F3, and F4 shown in the upper left of Figure 1 are not part of the light beam FE. The projection of the light beam FE includes an upper cutoff C with a raised section R. The portion of the light beam to the left of the raised section R illuminates less high than the portion of the light beam to the right of the raised section R. The lighting device is thus intended for use on a motor vehicle designed for right-hand traffic.Advantageously, small images, such as those corresponding to shape F1, are projected around the R-shaped bump to create a bump with sharp, precise contours. Larger images, such as those corresponding to shape F4, can be projected into the lower part of the illumination beam, since the precision requirements are lower in this part of the beam.

[0034] The collector 4 is now described in more detail with reference to Figures 2, 5, and 6. The collector 4 comprises a first elliptical reflecting surface 41 and a second parabolic reflecting surface 42. The first reflecting surface 41 is positioned upstream of the second reflecting surface 42, following the direction of propagation of the light rays from the light source 2. The light rays from the light source are therefore intended to be reflected first by the first reflecting surface 41, then by the second reflecting surface 42, before passing through the microlens array 3.

[0035] The first reflective surface 41 can be arranged on a first reflector. Similarly, the second reflective surface 4 can be arranged on a second reflector. The first and second reflectors are reflective optical components. They may, for example, comprise a body made of plastic material and be provided with a reflective coating. According to one embodiment of the invention, the first and second reflectors may form a single optical component whose body is obtained by molding.

[0036] The term "elliptical" generally applies to surfaces with two foci, that is, two areas of convergence for light rays such that the light rays emitted by a light source located at one of the two convergence areas converge, after reflection from the elliptical surface, towards the other convergence area. The convergence areas can be points or defined by a small volume, for example, a volume whose largest dimension is at most 5 times the dimensions of the emitting surface of the light source. Furthermore, the two convergence areas are located close to the elliptical surface, specifically within a volume whose dimensions are less than 10 times, and particularly less than 5 times, the largest dimension of the elliptical surface, surrounding said surface.In other words, the distance between each of the two convergence zones and the elliptical surface is at most 10 times, and specifically at most 5 times, the largest dimension of the elliptical surface. Thus, an "elliptical" surface encompasses a surface whose shape corresponds exactly to the geometric definition of an elliptical surface, but also a surface whose shape differs slightly from this geometric definition, provided that this surface includes two convergence zones as defined above.

[0037] The term "parabolic" generally applies to surfaces with a single focus, meaning a single area where light rays converge. Light rays emitted by a light source located at this point of convergence are projected over a great distance after reflection from the parabolic surface. As with an elliptical surface, the single point of convergence can be a point and defined by a small volume, for example, a volume whose largest dimension is at most five times the dimensions of the light source's emitting surface. "Projected over a great distance" means that these light rays do not converge at a point closer than ten times the largest dimension of the parabolic surface.In other words, light rays from a light source positioned at the level of the unique convergence zone and then reflected by a parabolic surface do not converge or, if they converge towards a convergence zone, this convergence zone is located at a distance from the parabolic surface greater than or equal to ten times the largest dimension of the parabolic surface, whether this convergence zone is real (located downstream of the reflector in the direction of propagation of the light) or virtual (located behind the reflector by extending the reflected rays in the opposite direction of their propagation).

[0038] The first reflecting surface 41 therefore comprises a first focal zone Z1, or convergence zone Z1, and a second focal zone Z2, or convergence zone Z2. The two convergence zones Z1 and Z2 are positioned on the same side of the first reflecting surface 41. The second reflecting surface 42 thus comprises a single focal zone ZC, or convergence zone ZC. The light source 2 is positioned at the first focal zone Z1 of the first reflecting surface 41; that is, at least one point on the emitting surface of the light source lies within the convergence zone Z1. The emitting surface is preferably oriented towards the first reflecting surface 41.

[0039] The single focal zone ZC of the second reflecting surface 42 is positioned at the level of the second focal zone Z2 of the first reflecting surface 41. In particular, the single focal zone ZC and the second focal zone Z2 can coincide, or at least share at least one point in common. The collector 4 is thus configured to project an image of the emitting surface of the light source to infinity. The light beam from the collimator 4 is therefore a collimated beam. The term "collimated beam" means that the beam can have an angular aperture, taking into account the geometric dimensions of the various elements, notably the dimensions of the light source 2 and the focal lengths of the first reflecting surface 41 and the second reflecting surface 42. By way of non-limiting example, the angular aperture is less than 5° around an average direction, i.e., less than 10° in total.Thus, the collimated beam corresponds to an angular image of the light source 2, that is, an image in which the geometric dimensions of the light source are converted into angular dimensions. Consequently, each microlens 33 receives light rays corresponding to this angular image of the light source 2, in order to project it into the illumination beam. It should be noted that, for simplification and to ensure readability, only light rays originating from a single specific point of the light source located on the convergence zone Z1 of the first reflection surface 41 are shown in the diagram, so that these rays are parallel to each other and parallel to the illumination axis X after projection by the collimator 4. This schematic representation is therefore not exhaustive.

[0040] A first optical axis D1 can be defined as the axis passing through the first focal zone Z1 and the second focal zone Z2 of the first reflecting surface 41, specifically through the center of the first focal zone Z1 and the center of the second focal zone Z2. A second optical axis D2 can also be defined as the axis passing through the single focal zone ZC and parallel to the axis of propagation of light rays reflected by a light source positioned at the single focal zone ZC. The second optical axis D2 is, in particular, parallel to the illumination axis X.

[0041] The angle A1 formed between the first optical axis D1 and the second optical axis D2 is defined as the smallest angle between these two axes. The closer the angle A1 formed between the first optical axis D1 and the second optical axis D2 is to 90°, the more compact the collector 4 will be along the illumination axis X. According to the embodiment illustrated in the figure, the angle A1 formed between axes D1 and D2 is equal to 90°, which allows for optimal compactness along the illumination axis X. However, the compactness of such a collector may be reduced along axes perpendicular to the illumination axis X. In general, this is not a problem for the design of a lighting system for a motor vehicle, as motor vehicles primarily lack available space in the longitudinal direction. Alternatively, the angle A1 formed between axes D1 and D2 could be different from 90°, while being greater than or equal to 45°, or preferably greater than or equal to 60°.This results in a reduction in size along the X lighting axis, while limiting the increase in size along axes perpendicular to the X lighting axis.

[0042] According to the illustrated embodiment, the reflecting surfaces 41 and 42 are positioned such that at least a portion of the light rays from the light source 2 undergo a first reflection at 90° or at an angle close to 90° on the first reflection, and then a second reflection at 90° or at an angle close to 90° on the second reflection. In Figures 2, 5, and 6, arrows F illustrate the path followed by the light rays.

[0043] As noted, and as illustrated in Figures 5 and 6, the reflecting surfaces 41 and 42 can advantageously be confined to the surfaces intended to receive light rays. This optimizes the size and mass of the lighting device. In Figure 5, reflecting surfaces 41 and 42 larger than necessary have been drawn, solely for the purpose of explaining the invention.

[0044] Advantageously, the light device 1 may further include a correcting lens 5 interposed between the first reflecting surface 41 and the second reflecting surface 42 along the path of the light rays emanating from the light source 2. The correcting lens 5 is an optical element configured to improve the sharpness of the image projected by the collector 4, in particular by correcting aberrations created by the reflecting surfaces 41 and 42. The correcting lens 5 may be a transparent element designed to allow light rays to pass through it. The correcting lens 5 may, for example, be made of transparent plastic and may be obtained by molding. The correcting lens 5 may, in particular, include an entrance face 51, or entrance diopter 51, and an exit face 52, or exit diopter 52.The specific shape of the inlet face 51 and the outlet face 52 can be calculated based on the defects to be corrected, for example, using optical simulation software familiar to those skilled in the art. The inlet face 51 and the outlet face 52 are generally non-planar surfaces.

[0045] The corrective lens 5 can be positioned between the first reflecting surface 41 and the second reflecting surface 42 along the path of the light rays. This arrangement allows for a relatively compact lighting device. In particular, the corrective lens 5 can be positioned approximately at the focal zones Z2 and ZC. The entrance face 51 and the exit face 52 can be positioned upstream and downstream of the focal zones Z2 and ZC, respectively. Alternatively, the corrective lens 5 could also be positioned at another location along the path of the light rays, for example, between the second reflecting surface 42 and the microlens array 3.

[0046] Figure 1 illustrates a set of isolux curves obtained with the collector 4 without the corrector lens 5 when it is used with a square emitting surface. Figure 2 illustrates a set of isolux curves obtained with the same collector 4 and the same emitting surface, but equipped with the corrector lens 5. These isolux curves can be obtained by projecting the light beam onto a screen extending perpendicularly to the illumination axis X, for example, 25 meters from the light source, this distance being approximated as infinite. These curves are obtained with the collector 4, and where applicable, the corrector lens 5, with the microlens array removed. Thus, these figures correspond to the image of the emitting surface of the light source 2 projected to infinity by the collector 4, and they are representative of the shape and angular dimensions of this image.On the first image, the isolux curves are relatively spread out, whereas they are more tightly packed on the second. The image IC2 projected by the collector 4 equipped with the corrector lens 5 therefore has sharper edges, that is to say, better defined edges, than the image IC1 projected by the same collector 4 without the corrector lens 5. Furthermore, by placing a diaphragm at the level of a microlens of the microlens array, the diaphragm having a size similar to that of said microlens, the collimated beam, observed under the same conditions as those of Figures 7 and 8, would have a shape similar to those shown in said Figures 7 and 8, respectively. Consequently, since the microlenses 33 each receive a sharper angular image of the light source when the collector 4 is equipped with the corrector lens 5, they each project a sharper image, possibly anamorphic, into the illumination beam.Advantageously, it is primarily the upper edge Bs and at least one left lateral edge Bg or one right lateral edge Bd that exhibit sharper edges. As explained previously, it is not necessary for all edges of the image to be sharp to project a beam of light with a cutoff featuring a raised edge. In particular, the corrector lens 5 can be optimized to improve the sharpness of the left lateral edge Bg and the upper edge Bs of the image projected by the collector 4 onto the microlens array 3 if the light-emitting device is intended for use in a right-hand drive vehicle. Similarly, the corrector lens 5 can be optimized to improve the sharpness of the right lateral edge Bg and the upper edge Bs of the image projected by the collector 4 onto the microlens array 3 if the light-emitting device is intended for use in a left-hand drive vehicle.By focusing on improving the sharpness of only a portion of the image edges, a more significant improvement in edge sharpness is achieved than if the aim were to improve the sharpness of all edges. If the same corrective lens 5 can optimize the sharpness of edges Bs, Bg, and Bd, then this lens can be used in both right-hand and left-hand traffic lighting systems.

[0047] For any point on a segment extending on either side of an edge of the image whose sharpness we wish to measure, the light intensity gradient is defined by the formula: G(α) = log(I (α + 0.05°)) – log(I (α - 0.05°)), where α is a polar angle of said point, and I is the intensity of the light beam at the angle α considered. The higher the gradient, the sharper the image. Thanks to the integration of the corrector lens 5, a light intensity gradient of 0.5 is achieved at the output of the collector 4, at the cutoff point, which makes it possible to consider achieving an average light intensity gradient of 0.3 at the output of the light device 1. We thus obtain a light beam with sharp and well-defined edges, which allows us to comply with automotive regulations relating to lighting.

[0048] Finally, thanks to the invention, we have a lighting device equipped with a microlens matrix which is more compact along its lighting axis, and which allows us to project an image sharp enough to perform a "dipped beam" type lighting function.

Claims

A lighting device (1) for a motor vehicle, comprising: - a light source (2), - a microlens array (3), and - a collector (4) configured to project an image of the light source onto an input face (31) of the microlens array, characterized in that the collector comprises: - a first elliptical reflecting surface (41), the first reflecting surface comprising a first focal zone (Z1) and a second focal zone (Z2), and - a second parabolic reflecting surface (42), the second reflecting surface comprising a single focal zone (ZC), the light source being positioned at the level of the first focal zone of the first reflecting surface, the single focal zone of the second reflecting surface being positioned at the level of the second focal zone of the first reflecting surface. A luminous device according to the preceding claim, characterized in that the first reflecting surface (41) comprises a first optical axis (D1) passing through the first focal zone (Z1) and through the second focal zone (Z2) of the first reflecting surface, in that the second reflecting surface (42) comprises a second optical axis (D2) parallel to the axis of propagation of the light rays reflected by the second reflecting surface, and in that the first optical axis forms with the second optical axis an angle (A1) greater than or equal to 45°, or even greater than or equal to 60°, or even substantially equal to 90°. A lighting device according to any one of the preceding claims, characterized in that the light source comprises a single electroluminescent semiconductor element. A lighting device according to one of the preceding claims, characterized in that the light source comprises an emitting surface of substantially square or substantially rectangular shape. A lighting device according to one of the preceding claims, characterized in that it comprises a corrective lens (5) interposed between the first reflecting surface (41) and the second reflecting surface (42) along the path of the light rays from the light source. A luminous device according to the preceding claim, characterized in that the corrective lens (5) comprises an entrance surface positioned between the first reflection surface (41) and the second focal zone (Z2) of the first reflection surface. A lighting device according to claim 4 or 5, characterized in that: - the corrective lens (5) is optimized to improve the sharpness of a left lateral edge (Bg) and a top edge (Bs) of the image projected by the collector (4) onto the microlens array (3) if the lighting device is intended to equip a motor vehicle for right-hand traffic, or in that - the corrective lens is optimized to improve the sharpness of a right lateral edge (Bd) and a top edge (Bs) of the image projected by the collector (4) onto the microlens array (3) if the lighting device is intended to equip a motor vehicle for left-hand traffic. A lighting device according to any one of the preceding claims, characterized in that it comprises a single monolithic component, in particular, obtained by plastic injection, the first reflective surface and the second reflective surface being formed on said monolithic component. A lighting device according to one of the preceding claims, characterized in that it is configured to produce a dipped beam of lighting, the lighting beam comprising a cut (C) provided with a bump (R).

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