Patent Application
20250137611
The present invention relates to a light module intended to be incorporated into a lighting device for a motor vehicle.
Lighting devices are known to heat up when they are being used, on account of the heat released by light sources that are present therein. The temperature within the lighting device rises, and this may have an impact on elements that are contained in this device. For example, it is common for lens accommodated in the lighting device, when the latter is used to project a light beam, to expand with the increase in temperature.
The thermal expansion of the lenses may cause the focus, or the focal plane, associated with these lenses to shift. When the lighting device is designed to project a pattern, the shifted focal plane no longer lies at the level of the pattern. The projected image therefore loses its sharpness. In other words, the quality of the projected image is compromised. This phenomenon is also known as defocusing.
In order to overcome this problem, the lenses are manufactured from glass, a material which is thermally stable and withstands the increase in temperature well. However, these lenses have a high weight and are expensive. Moreover, manufacturing the lenses from glass is complex. This is because, for use in the lights of a motor vehicle, a portion of the glass lenses is often made of plastic, this needing to be overmoulded over the glass and complicating the manufacturing process.
Another proposed solution is to install the lens or lenses in a support element which withstands the high temperature well in order to prevent the expansion of the lenses. Specifically, the support element clamps the perimeter of the lens or of the set of lenses. It thus remains fixed in spite of the increase in temperature and applies a load to the lens or to the set of lenses such that they cannot expand. However, this load localized at the perimeter of the lenses shifts the deformation caused by the thermal expansion to a load-free zone, notably the central zone at which the optical surface of the lenses is located. Consequently, the optical surface is deformed more extensively than if there were no support element. This deformation is difficult to control and may have uncertain consequences on the location of the focal plane.
Given the foregoing, an objective of the invention is to design a light module, intended to be mounted in a lighting device, which reduces, or even eliminates, the problem of defocusing caused by the thermal expansion of the optical elements. Such a light module also meets the requirements relating to the manufacturing cost and weight while being simple to implement.
With this objective in mind, the invention provides a light module comprising:
According to the invention, the second support element is arranged so as to allow the thermal expansion of the projection optic, causing the focal plane to shift in a first direction.
Moreover, the first support element exhibits a first coefficient of thermal expansion, the second support element exhibiting a second coefficient of thermal expansion which is different from the first coefficient of thermal expansion. Lastly, the first support element is connected on one side to the fixed mount and on the other side to the second support element so as to shift the second support element during the deformation of the first support element in a second direction opposite to the first direction.
In this case, the fixed mount serves as a frame of reference. It reacts very little, if at all, to the variation in the temperature in the light module. By way of example, the fixed mount may be made of an inert material, which is insensitive to temperature. The second support element carries the projection optic. For example, the second support element comprises a recess in which the projection optic is installed. Lastly, the first support element acts as an intermediate part between the fixed mount and the second support element.
In the light module proposed, the projection optic is free to deform by thermal expansion on account of the increase in the temperature within the light module. The shifting of the focal plane brought about by this deformation is compensated by the holding member.
Specifically, given that the holding member does not block the expansion of the projection optic, the focal plane can move within a defined perimeter. However, the second element of the holding member is designed to orient the shifting of the focal plane in a given direction. In parallel, the holding member is also deformed, under the effect of the temperature, so as to shift the projection optic in an opposite direction to the direction in which the focal plane is shifted.
Consequently, the focal plane is located close to or in the vicinity of the location it was at before the increase in temperature, in spite of its shifting caused by the thermal expansion of the projection optic. In other words, the phenomenon of defocusing is compensated in the light module proposed.
Thus, the projected image always remains sharp for good image quality, regardless of the operating time of the light module.
Furthermore, since the light module is capable of compensating the defocusing brought about by the thermal expansion, it is conceivable to use a constituent material of the projection optic which is sensitive to the variation in temperature but, on the other hand, is inexpensive. By way of example, the projection optic may be made of polycarbonates (PC), of polymethyl methacrylate (PMMA), of cycloolefin polymer (COP), for example of the brand Zeonex®. Nevertheless, the holding member proposed is quite suitable for a glass projection optic.
In the present document, the projection optic creates a real, and possibly anamorphic, image of a part of the module, for example the source itself, or of an intermediate image of the source, at a very large (finite or infinite) distance in comparison with the dimensions of the module (with a ratio of the order of at least 30, preferably 100). This projection optic may consist of one or more reflectors, or of one or more lenses, or one or more light guides, or even of a combination of these possibilities.
The light module according to the invention may optionally have one or more of the following features:
A further subject of the invention is a motor vehicle lighting device comprising a light module according to the invention.
By way of example, the lighting device provides an auxiliary function of lighting the space situated on either side of the vehicle.
According to one embodiment, the lighting device comprises a housing. The fixed mount is connected to the housing by suitable fixing means
Further innovative features and advantages will become apparent from the following description, which is given by way of non-limiting indication, with reference to the appended drawings, in which:
With reference to these figures, notably to
The lighting device acts as a side lighting means for the space situated next to the front and rear entrance doors.
In
The light source 2 is in this case an LED (short for “light-emitting diode”). Other types of light source are conceivable. The light source 2 may comprise one or more LEDs.
In the example illustrated, the projection optic 3 has a focal plane F and it is made up of a plurality of lenses 30 which are stacked one on top of another. There are four lenses here.
Each of the lenses 30 comprises a central zone 311 with dioptric surfaces that realize an optical function and a peripheral zone 312 surrounding the central zone 311. The dioptric surfaces are configured to project the rays output by the light source 2 while limiting optical aberrations such as distortion. The projection optic 3 is referred to as set 3 of lenses below.
The peripheral zone 312 is provided with engagement means intended to cooperate with complementary engagement means in the peripheral zone of the adjacent lens. By way of example, engagement means may comprise a groove or a rib.
The slide 5 is in this case a transparent plate 53 having, by way of illustration, a square cross section. The slide 5 may be made of glass, for example of borosilicate glass, or of plastic, for example of polyethylene terephthalate (PET).
The slide 5 has a first face 51 and a second face 52. The slide is placed in the light module 1 such that the first face 51 is oriented towards the set 3 of lenses and such that the second face 52 is oriented towards the light source 2. The first face 51 is also known as the downstream face and the second face 52 is also known as the upstream face. The terms “upstream” and “downstream” are defined in the direction of propagation of light in the light module 1.
In the example illustrated, the fixed mount 7 acts as a support for the light source 2 and for the slide 5. In this case, the fixed mount 7 comprises a base 20 on which the light source 2 is mounted. The base 20 may be a printed circuit board (or PCB).
The fixed mount also comprises a frame 50 carrying the slide 5 and a collimator 6 placed between the light source 2 and the slide 5. In this case, the collimator 6 is an integral part of the frame 50. The collimator 6 comprises an upstream face 61 disposed facing the light source 2 and a downstream face 62 disposed facing the slide 5.
In this example, the frame 50 is secured to the base 20 by means of two fixing tabs 51 and two pins 52. Specifically, the fixing tabs 51 are in abutment against a secondary face 22 of the base 20, while the pins 52 are engaged in corresponding holes made in the base 20. In this way, the base 20 and the frame 50 form a block that constitutes the fixed mount 7.
The projection optic 3 is connected to the fixed mount 7 by way of the holding member 4. In this case, the holding member 4 acts both as a support for the lenses 30 and as a means for positioning the lenses with respect to the slide 5.
According to the invention and as in the example illustrated, the holding member 4 comprises a first support element 41 and a second support element 42.
The first support element 41 is the intermediate part which connects the fixed mount 7 to the second support element 42. Specifically, the first support element 41 is formed in this case by a cylindrical sleeve interposed between the fixed mount 7 and the second support element 42. Said first element is also known as a barrel in the vocabulary of those skilled in the art. The first support element 41 comprises engagement tabs 412 which are intended to be inserted into slots 513 made in the fixed mount 7 in order to assemble these two elements.
Once assembled, the first support element 41 is in contact with the fixed mount 7 at its first end 411 oriented towards the fixed mount 7. The first end 411 is also known as the first contact zone 411.
In this case, the first contact zone 411 comprises a plurality of contact portions. Some of these are situated at the same level as the first face 51 of the slide 5. Some others are located at a higher level than the slide, notably the contact portions between the first support element 41 and the shoulder of the fixing tabs 51 of the frame 50. In other words, the connection between the first contact zone 411 and the first face 51 may be realized at different levels.
In the example illustrated, the first support element 41 is connected to the second support element 42 at its second end 412 situated at the opposite end from the first end 411. In this case, the first support element 41 is in contact with the second support element 42 by way of a layer of adhesive which connects these two elements together. Other connecting means may be envisaged. The joining together of the first support element 41 and the second support element 42 by adhesive bonding makes it possible to easily adjust the position of the focal plane F of the set 3 of lenses with respect to the slide 5.
In this case, the second support element 42 comprises two separate parts that are fitted one in the other so as to form an accommodating space for the set 3 of lenses. The second support element 42 is also known as the lens box.
Specifically, the first part 421 comprises a hollow cylindrical body which is open on both sides. However, the opening on one of the sides is smaller than that on the other side. Specifically, the first side of the first part 421, which is the one oriented in the direction of the light source, comprises an inwardly folded edge so as to create an annular seat 423. In this case, the annular seat 423 has a shape complementary to the shape of the peripheral zone 311 of the lens 30 which is in direct contact with this seat. In this way, the annular seat 423 conforms perfectly to the shape of the peripheral zone 311 in order to ensure correct retention between the first part 421 and the lens 30. The annular seat 423 delimits a first opening 425, the diameter of which corresponds to the diameter of the central zone 312 of the lenses 30.
The second side of the first part 421, which is on the opposite side from the first side, comprises a flange 424 which rests on the second end 412 of the first support element 41 and is fixed thereto by suitable means, for example a UV-crosslinkable adhesive, a thermal adhesive or a combination of these two types of adhesive. The flange 424 defines a second opening 426 having a diameter larger than the diameter of the first opening 425. The second opening 426 is intended to be wide enough to receive the second part 422 of the second support element 42.
In this case, the second part 422 also comprises an open-ended hollow cylindrical body. The second part 422 is partially fitted in the first part 421. The free end, which is the end that is not fitted, of the second part 422 comprises an inwardly folded edge 428 which bears on a diaphragm 33. The latter is part of the set 3 of lenses and comprises an opening which defines the optical surface of the set 3 of lenses.
The second part 422 is designed such that the folded edge 428 exhibits elastic deformation behavior, meaning that the edge 428 tends to return to its initial position when it is deformed. In this case, the second part 422 has a sufficiently small thickness to confer the elastic behavior on the edge 428. The edge 428 as shown in
The second part 422 designed in this way is also known as the elastically deformable member. In addition, the elastic deformation of the edge 428 allows the set 3 of lenses to expand when the temperature of the light module increases. Specifically, the edge 428 is raised under the effect of the pushing of the set 3 of lenses when the latter expands.
Once the first part 421 and the second part 422 are assembled, these two parts form a housing in which the set 3 of lenses is accommodated. Said housing constitutes the second support element 42.
In the example illustrated, each of the set 3 of lenses, the first support element 41 and the second element 42 is subject to expansion when the temperature varies. In this case, each of these elements is made from a material having a positive coefficient of thermal expansion, meaning that these elements expand and their size increases when the temperature increases. However, the coefficients of thermal expansion of these elements are different, specifically so as to contribute, with the above-described assembly, to limiting the defocusing of the projection optic. In other words, the arrangement of the above-described light module and the different composition of certain elements in this light module make it possible to keep the focal plane F at a desired location, in this case substantially at the first face 51 of the slide 5, in spite of the increase in temperature in the module.
The operating principle of the concept presented will now be explained in detail with reference to
In the example illustrated, the first support element 41 is made of a material that exhibits a first coefficient of thermal expansion α1. The second support element 42 is made of a material that exhibits a second coefficient of thermal expansion α2. The set 3 of lenses exhibits a third coefficient of thermal expansion α3. In this case, these coefficients are classified in decreasing order of their value as follows:
If the holding member 4 were not present, the expansion of the set 3 of lenses caused by an increase in the temperature in the module would have shifted the focal plane F in the direction of the fixed mount 7 along the arrow D illustrated in
The distance by which the focal plane F shifts, known as the second distance d2, depends on the variation in the temperature:
In the light module of the example illustrated, when the temperature increases, the set 3 of lenses, disposed in the holding member 4, expands in a direction away from the fixed mount 7 as indicated by the arrow C illustrated in
The expansion of the set 3 of lenses causes the focal plane F to shift. In practice, and by way of non-limiting example, the shifting of the focal plane F, at a given temperature variation, is calculated by a thermo-optical simulation using the bearing surface between the first element and the fixed mount as reference point. This calculation can be carried out for each point in the range of operating temperatures.
In the knowledge of the behavior of the set 3 of lenses and the shifting of the focal plane, the first and second elements 41 and 42 are designed to position the focal plane F at the first face 51 of the slide in spite of the expansion. Specifically, the difference between the coefficient of thermal expansion of the first element 41 (α1) and that of the second element 42 (α2) needs to be large enough to shift the set 3 of lenses in an opposite direction to the shifting of the focal plane F and by a distance substantially equal to the distance by which the focal plane F shifts.
Specifically, when the temperature increases to the value T1, the first support element 41 lengthens in the direction away from the fixed mount 7, indicated by the arrow A in
In parallel, the second support element 42 lengthens in the direction of the fixed mount 7, indicated by the arrow B. In this case, it is the first part 421 which lengthens towards the fixed mount 7, since the other end of the first part is connected to the first support element 41. The lengthening of the second support element 42 reflects the expansion of the set 3 of lenses. The second support element 42 has an intermediate role which both allows the set 3 to expand and which is shifted by the deformation of the first support element. This shifting moves the set 3 of lenses in the opposite direction to the movement of the focal plane F. The value of the distance moved depends on the coefficients of thermal expansion of the first and second support elements 41 and 42.
Specifically, as a result of the deformation of the first support element 41 and of the second support element 42, the set 3 of lenses is shifted in the direction away from the fixed mount 7, indicated by the arrow E, by a first distance d1. This distance depends on the lengthening of each of the first and second support elements 41, 42 and on their respective coefficients of thermal expansion:
The focal plane F associated with the set 3 of lenses is shifted in the same way as this set, that is to say in the direction away from the fixed mount 7 and by a value of the first distance d1.
Thus, in order to have the focal plane F positioned relatively close to the initial location, or even at the same location as before the increase in the temperature, the rising of the set 3 of lenses needs to compensate for the shifting of the focal plane F caused by the phenomenon of expansion.
In other words, in addition to the fact that the set 3 of lenses and the focal plane F shift in two opposite directions, the first distance d1 and the second distance d2 need to be substantially equal: d1=d2 (+/−10%). This is obtained through a suitable choice of the first and second coefficients of thermal expansion α1 and α2.
The result obtained is illustrated in
Consequently, the light module 1 as described solves the problem of defocusing encountered when the temperature in the module increases. Since the focal plane is kept at the first face of the slide, the projection of the pattern is displayed sharply during the use of the module, regardless of the duration.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2107569 | Jul 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/069327 | 7/11/2022 | WO |
