Abstract
A cover lens for a vehicle lighting device is provided, and includes a visual section which is transparent and designated to form the light exit aperture of the lighting device. The cover lens also includes a blank section which is opaque and/or which is designated to be invisible from the exterior of the lighting device. The blank section includes at least one condensation area. The wall thickness of the condensation area is lower than the wall thickness of the visual section.
Claims
1. A cover lens for a vehicle lighting device comprising, the cover lens comprising: a visual section which is transparent and forms a light exit aperture of the lighting device, and a blank section which is opaque and/or which is invisible from an exterior of the lighting device, the blank section including at least one condensation area, wherein a wall thickness of the condensation area is lower than a wall thickness of the visual section.
2. The cover lens according to claim 1, wherein the condensation area is arranged below the visual section with respect to a designated mounting position of the lighting device.
3. The cover lens according to claim 1, wherein the wall thickness of the condensation area amounts to between 1% and 90% of the wall thickness of the visual section.
4. The cover lens according to claim 1, wherein the blank section comprises several condensation areas arranged peripherally around the visual section.
5. The cover lens according to claim 4, wherein the wall thickness varies among the different condensation areas.
6. The cover lens according to claim 1, wherein the condensation area features a hexagonal contour.
7. The cover lens according to claim 1, wherein the condensation area features a surface structure dedicated to increase the wettability with water.
8. A vehicle lighting device comprising a cover lens according to claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Reference is now made more particularly to the drawings, which illustrate the best presently known mode of carrying out the invention and wherein similar reference characters indicate the same parts throughout the views.
[0018] FIG. 1 is a graph of the dew point curve of water in air.
[0019] FIG. 2a is a sketch in front view of an inventive cover lens.
[0020] FIG. 2b is cross-sections of alternative embodiments related to FIG. 2a.
[0021] FIG. 3 is a sketch in front view of a second embodiment of the inventive cover lens.
[0022] FIG. 4 is a sketch in front view of a third embodiment of the inventive cover lens.
DETAILED DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows the dew point curve of water in air at sea level pressure, i.e. the saturation vapour pressure ps as a function of the temperature T and the water vapour partial pressure p. The dew point curve separates the liquid water phase l from the water vapour phase v.
[0024] In the following, the bedewing properties of the inventive cover lens shall be discussed exemplarily in the context of the bedewing test for vehicle head lights according to the FMVSS 108 standard. In this test, the lighting device is subject to a conditioning stage, after which it is prepared in the initial condition s0 as depicted in FIG. 1, i.e. featuring a temperature of T=38° C. and humidity of about 80% inside the lighting device corresponding to a water vapour partial pressure of p=5.3 kPa. In the following, the lighting device under test is put into a wind tunnel and subject to a constant air stream with a temperature of T=26° C. Starting from the same initial condition s0, the local air volumes at the inner surfaces of the visual section and the condensation area evolve along the different phase space trajectories x1 and x20, respectively. Due to the higher cooling rates at the thin-walled condensation area, the local temperature there reaches the dew point around T=34° C. at first, and condensation of water from the supersaturated water vapour sets in. In the following, the cooling rates at the condensation area are for instance high enough to pin the related trajectory x20 right to the dew point curve, thus permanently bedewing the inner surface of the condensation area and in turn lowering the humidity of the remaining air volume in the interior of the lighting device. At the inner surface of the visual section, the air temperature remains higher during the (early) cooling stage compared to the condensation area and the temperature of T=34° C., corresponding to the initial dew point temperature, is only reached after condensation has already set in at the condensation area, i.e. at a point in time, in which the humidity of the air is already significantly lowered. Consequently, water partial pressure remains at a subcritical level at the inner surface of the visual section, and with the condensation area constantly trapping more water from the ambient, phase space trajectory x1 of the air volume at the inner surface of the visual section runs through the vapour phase v during the entire test procedure. Finally, all condensed water is confined to the condensation section, which is invisible from the exterior of the lighting device, and the visual section is free of any bedewing.
[0025] FIG. 2a shows a sketch in front view of an inventive cover lens 100 for a vehicle lighting device comprising a visual section 1, which is transparent and designated to form the light exit aperture of the lighting device, and a blank section 2, which is opaque and/or which is designated to be invisible from the exterior of the lighting device. Especially, the blank section 2 may be covered by the housing of the lighting device or by a portion of the vehicle body. The cover lens 100 may be injection moulded as one piece of equal material or the visual section 1 and the blank section 2 are manufactured and joint in a multiple-step process, especially from transparent and opaque materials, respectively. The blank section 2 comprises the two condensation areas 20 below and above the visual section 1, wherein the wall thickness of the condensation areas, i.e. the thickness along the direction perpendicular to the plane of the sketch, is lower than the wall thickness of the visual section 1.
[0026] FIG. 2b shows cross-sections of alternative embodiments of the schematic cover lens 100 of FIG. 2a, wherein the cross-sections correspond to the line AA in FIG. 2a. The embodiment on the left-hand side features condensation areas 2 with a wall thickness t20 corresponding to 50% of the wall thickness t1 of the visual section 1. The embodiment on the right-hand side features condensation areas 2 with a wall thickness t20 corresponding to 25% of the wall thickness t1 of the visual section 1, and furthermore, the condensation areas 20 protrude over the visual section 1. Through such protuberance, the condensation areas 20 are possibly more exposed to cooling air streams during vehicle operation or test procedure, so that the bedewing condition is further improved.
[0027] FIG. 3 and FIG. 4 show sketches in front view of further preferred embodiments of the inventive cover lens 100 dedicated for a vehicle head light. The cover lens 100 features a free-form geometry with a foremost wedge-shaped visual section 1 and a rearwardly curved blank section 2.
[0028] In FIG. 3 the four condensation sections 20 are arranged below the visual section 1 in order to prevent condensed water from running towards the visual section 1. The cover lens 100 of FIG. 4 also features additional condensation sections 20 above the visual section 1 to yield a peripheral arrangement of condensation sections 20. The lateral size and contour shape vary among the different condensation sections 20 and can be adjusted e.g. according to the geometry and dimensions of the corresponding lighting device. A stiffening effect results especially from the hexagonal shapes of the two condensation sections 20 on the bottom portion of the blank section 2 in FIG. 4.
[0029] The present invention is not limited by the embodiments described above, which are presented as examples only and can be modified in various ways within the scope of protection defined by the appending patent claims.
LIST OF NUMERALS
[0030] 100 cover lens
[0031] 1 visual section
[0032] 2 blank section
[0033] 20 condensation area
[0034] t1 wall thickness of visual section
[0035] t20 wall thickness of condensation area
[0036] T temperature
[0037] p water vapour partial pressure
[0038] p.sub.s saturation vapour pressure
[0039] l liquid phase
[0040] v vapour phase
[0041] s0 initial condition
[0042] x1 phase space trajectory
[0043] x20 phase space trajectory
