Patent Application
20140016342
The present disclosure relates to particular optical geometries for low-beam and high-beam headlights.
Automobiles are equipped with both low-beam and high-beam outputs from their headlights. The low-beam output is usually angled downward and slightly away from oncoming traffic, in order to reduce glare for oncoming vehicles on the opposite side of the road. The high-beam output is brighter and lacks the directional requirements of the low-beam output, and as such is suitable only when alone on the road. Because of the different angular requirements of the low-beam and high-beam outputs, switching between low and high beams is not as straightforward as making the headlamp brighter or dimmer.
In many cases, automobiles are typically equipped with separate headlamps for the low-beam and high-beam outputs. The low-beam and high-beam headlamps are mounted adjacent to each other on the front of vehicles, and are aimed appropriately to meet the angular requirements of the low and high beams.
Historically, most of the headlamp designs have used incandescent bulbs, which have a limited lifetime and produce a relatively large amount of heat. In recent years, use of incandescent bulbs has been giving way to use of light emitting diodes (LEDs) as the light source in many lighting and illumination applications. In comparison, LEDs have a much longer lifetime and produce much less heat than their incandescent counterparts.
Accordingly, there exists an ongoing need for LED-based headlamp designs that reduce wasted light and improve the efficiency in converting output light from the LEDs into the low-beam light and high-beam light.
An embodiment is a headlight 20. The headlight includes a low-beam housing 31. The low-beam housing 31 includes a generally horizontal longitudinal axis 39. The low-beam housing 31 receives light from an LED array 33 and delivers the light to a transmissive lens 32. A receiving face of the lens 32 and an emission face of the LED array 33 both have generally rectangular perimeters with generally horizontal and vertical peripheral edges. The low-beam housing 31 includes a top inward-facing reflector 12 extending from a top peripheral edge of the LED array 33 to a top peripheral edge of the lens 32. The low-beam housing 31 also includes two lateral inward-facing reflectors 2, 10. Each lateral inward-facing reflector 2, 10 extends from a side peripheral edge of the LED array 33 to a corresponding side peripheral edge of the lens 32. Each lateral inward-facing reflector 2, 10 intersects the top inward-facing reflector 12 along a curve 1, 11. The low-beam housing 31 also includes a first upward-facing reflector 34 extending away from the LED array 33 toward the lens 32. The first upward-facing reflector 34 is generally planar, generally horizontal, and disposed below the longitudinal axis 39. The first upward-facing reflector 34 receives low-beam light from the LED array 33 and reflects the low-beam light upward toward the lens 32 and toward the top inward-facing reflector 12.
The foregoing and other objects, features and advantages disclosed herein will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles disclosed herein.
In this document, the directional terms “up”, “down”, “top”, “bottom”, “side”, “lateral”, “longitudinal” and the like are used to describe the absolute and relative orientations of particular elements. For these descriptions, it is assumed that light exits through a “front” of the headlight, with a spatial distribution centered around a longitudinal axis that is generally perpendicular to the front of the headlight, and is generally parallel to the ground. These descriptions include the minor angular deviations from orthogonality that account for reducing glare for oncoming vehicles. It will be understood that while such descriptions provide orientations that occur in typical use, other orientations are certainly possible. The noted descriptive terms, as used herein, still apply if the headlight is pointed upward, downward, horizontally, or in any other suitable orientation.
A headlight 20 is disclosed, having separate low-beam and high beam housings 31, 41. The high-beam housing 41 includes four planar inward-facing reflectors 103, 106, 109, 112 in the shape of a pyramid, with the high-beam LED array 43 at the apex and a plano-convex high-beam lens 42 at the base. The low-beam housing 31 includes three planar inward-facing reflectors 12, 2, 10 along the top and lateral sides, similarly arranged as three sides of a pyramid. Unlike the high-beam housing 41, the low-beam housing 31 does not have a fourth side to the pyramid along its bottom edge, but instead has one or more planar, horizontal upward-facing reflectors 34, 35, disposed below the longitudinal axis 39 of the low-beam housing 31. Light propagating downward from the low-beam LED array 33 directly strikes either the incident face of the low-beam lens 32 or exactly one upward-facing reflector 34 or 35. When viewed from the front of the low-beam housing 31, the upward-facing reflectors 34, 35 resemble steps that descend from a lower edge of the low-beam LED array 33.
The above paragraph is merely a generalization of several of the elements and features described in detail below, and should not be construed as limiting in any way.
For this design, the low-beam and high-beam portions 30, 40 are configured as separate, independent units that reside next to each other in the front of a vehicle. It is typical practice, and is also a U.S. legal requirement, that the low-beams are outboard, at the edges of the vehicle, with the high-beams being adjacent to the low-beams toward the center of the vehicle or beneath the low-beams.
Both the low-beam 30 and high-beam 40 portions of the headlight 20 are arranged similarly. Each portion 30, 40 is arranged as discrete units, which may be manufactured and/or sold together, but will be discussed below as being separate. For each, the light originates at an LED array (not shown in
For both the low-beam 30 and high-beam 40 portions, the light emerges as a highly directional beam, with most of the light being directed directly in front of the vehicle, and with a prescribed falloff in various directions. The low-beams are designed to stay out of the eyes of oncoming drivers, so the low-beam output beam typically has a sharp angular cutoff between dark and bright portions. For vertical propagation angles, there is a particular angle (sometimes known as a horizon) above which there is generally no light and below which there is bright light, so that drivers may see the road in front of the vehicle. For horizontal propagation angles, there is usually a small angling away of the hot spot, toward the shoulder of the road, to keep the light of out of oncoming traffic. This angling away from true horizontal and/or directly in front of the vehicle is typically on the order of a few degrees. These angular requirements are typically built into law, and usually vary country-to-country. In general, these angular requirements are known and well-established. It is assumed that one of ordinary skill in the art is aware of these angular requirements, and suitably builds them into the headlights. For the purposes of this document, it will be assumed that the longitudinal axes 39, 49 of the low-beam 30 and high-beam 40 portions are taken to parallel, are “generally” horizontal and extend “generally” in front of the vehicle, even though in practice there may be these small angular deviations from “true” horizontal or “truly” in front of the vehicle. The term “generally” is intended to account for these small angular deviations, which are built into the pointing and legal requirements on the headlights.
There are several known ray-tracing programs that are commonly used to simulate the performance of the headlight and optimize the housings, lenses and LED geometries. For instance, the program LucidShape is computer aided designing software for lighting design tasks, and is commercially available from the company Brandenburg GmbH, located in Paderborn, Germany. Other known computer software may also be used. In general, one of ordinary skill in the art can use the software to alter and optimize the particular shape of the lenses 32, 42, for any particular reflector configuration. The optimization process is well-known to one of ordinary skill in the art, and it is assumed herein that for a given configuration of housings 31, 41, the convex sides of the lens 38, 48 may have their shapes optimized in software, during the simulation phase of the design, and may do so without undue experimentation.
We first describe the low-beam portion 30 in detail, followed by a description of the high-beam portion 40.
Light originates at a low-beam LED array 33, passes through a low-beam housing 31, in which it may undergo one or more reflections, enters a lens 32, and finally exits the lens 32 and the headlight 20. Most of the exiting light propagates at angles fairly close to the longitudinal axis 39 of the low-beam housing 31, as discussed above.
The low-beam LED array 33 may be a generally rectangular or square array of LEDs. The LEDs in a typical array are square or rectangular, with thin “dead” spaces of non-emission between the individual LEDs. The array 33 may have a square configuration, such as 2 by 2, 3 by 3, 4 by 4, and so forth. The array 33 may alternatively have a rectangular configuration, such as 1 by 2, 1 by 3, 1 by 4, 1 by 5, 2 by 3, 2 by 4, 3 by 4, and so forth. As a further alternative, the array may have an irregular shape, such a “plus” sign, a “T” shape, a generally circular or elongated footprint, and so forth. The LEDs in the array 33 may emit with a generally white light, and may be formed with a phosphorescent coating applied over a blue or violet emitter. Alternatively, the LEDs may be grouped in clusters, with each cluster having a red, green and blue LED. The differently colored LEDs in each cluster have relative brightnesses that are controlled electronically, so that that the combined red, green and blue light appears generally white to a human eye. In general, the structure and function of the low-beam LED array 33 is known.
For the specific design in
The emission pattern of the LED array 33 has an angular peak along the longitudinal axis 39, falls off at angles away the longitudinal axis 39, and falls to zero at angles perpendicular to the longitudinal axis 39. In other words, although most of the light propagates along the longitudinal axis 39 and directly strikes an incident face of the lens 32, smaller amount of light propagate slightly upward, and downward, and into/out of the page in
In the cross-section of
Along a top edge of the low-beam housing 31 is a so-called “top inward-facing reflector” 12, which may reflect rays that would otherwise miss the lens 32 back toward the lens 32. This reflector is discussed in more detail in the context of
In addition to the top inward-facing reflector 12, next to the LED array 33, just below the longitudinal axis 39, are two “upward facing reflectors” 34 and 35. When viewed from the front of the low-beam housing 31, the upward-facing reflectors 34, 35 resemble steps that descend from a lower edge of the low-beam LED array 33.
It is the intent of the upward-facing reflectors 34, 35 to reflect light that is propagating downward, which would have otherwise struck the lower half of the lens 32 or missed the lens entirely, and redirect it toward the upper half of the lens 32, or toward the top inward-facing reflector 12, which would in turn direct it toward the upper half of the lens 32.
The motivation for such a light redirection may be found from the design of the lens 32. Lens 32 is plano-convex, with a planar side 37 facing the low-beam housing 31, and a convex side facing away from the low-beam housing 31. A starting point in designing such a lens may be an aspheric collimating lens, but there may be significant warpage of the convex surface away from the starting point to achieve the desired performance. For the lens 32 of
There is a rule-of-thumb guideline for the size of upward-facing reflectors 34, 35. In general, it is intended that no downward-propagating light strikes the bottom side 6 of the low-beam housing 31, but in practice it is sufficient that most of the downward-propagating light is directed away from striking the bottom side 6 of the low-beam housing 31. This determines a maximum lateral extent of the second upward-facing reflector, or put more simply, this determines how far the second step “sticks out” toward the lens. In terms of the geometry of
Note that in some designs, only a single upward-facing reflector is used. In the designs of
Having explained the cross-sectional drawing of
At the center of the drawing is the low-beam LED array 33. Note that the view of
There are a series of surfaces and edges surrounding elements 33-36. Because these many surfaces may be a bit confusing at first glance, the surfaces and edges are numbered according to clock position, when viewed end-on from the front of the low-beam housing 31, as in
At 12 o'clock, the top inward-facing reflector 12 extends from a top peripheral edge of the LED array 33 to a top peripheral edge of the lens 32.
At 10 o'clock and 2 o'clock are two lateral inward-facing reflectors numbered, conveniently, as 2, 10. Each lateral inward-facing reflector 2, 10 extends from a side peripheral edge of the LED array 33 to a corresponding side peripheral edge of the lens 32.
Note that each lateral inward-facing reflector 2, 10 intersects the top inward-facing reflector 12 along a curve 1, 11. For the special case in which the reflectors 2, 10, 12 are all truly planar, the curves 1, 11 are lines. Note that even if there is some small curvature to the reflectors, it is intended that the reflectors meet in a relatively discontinuous corner, so that there is some “seam” between the reflectors.
Note that top inward-facing reflector 12 and the two lateral inward-facing reflectors 2, 10 may completely subtend a half-space within the low-beam housing 31 above the longitudinal axis 39.
The remaining surface 4, 6 and 8, which may completely subtend a half-space within the low-beam housing 31 below the longitudinal axis 39, are less interesting optically, because it is intended that no light strike these surfaces. Surfaces 4, 6 and 8 normally have a non-reflective finish. Surface 4 and 8 may be referred to as lateral sides of the low-beam housing 31, which meet the bottom side 6 of the low-beam housing 31 at respective curves of intersection 5 and 7. Note that surfaces 2 and 4 may simply be parts of the same plane but with different surface treatments, with the lateral inward-facing reflector 2 requiring a shinier surface than the lateral side 4. The curve of intersection 3 may simply be an edge of the shiny surface. A similar condition holds for curve 9.
Having discussed the low-beam portion 30, we now discuss the high-beam portion 40.
In general, the high-beam optics may be simpler than the low-beam optics, because there is no requirement for a sharp bright/dark edge. It is assumed that the high-beams are only used when there is no oncoming traffic, so that the high-beam light may freely extend above the horizon and into the opposite side of the road. The high-beam portion 40 is shown in cross-section in
The high-beam LED array 43 may be similar in function and construction to the low-beam LED array 33. Light from the high-beam LED array 43 is received by the high-beam housing 41, where it may pass directly through the housing 41 or undergo a reflection, refracts at the planar side 47 of plano-convex lens 42, and refracts out of the lens 42 at the convex side 48 of the lens 42. The high-beam longitudinal axis 49 may be parallel to the low-beam longitudinal axis 39, and both may coincide with a horizon.
Note that the convex side 48 of the lens 42 may have a slightly different shape than the convex side 38 of low-beam lens 32. Both may have originated using an aspheric collimator as a starting point, but each lens is typically optimized in performance for its particular use.
One difference between the low-beam and high-beam portions 30, 40 is that there is light passing through both top and bottom halves of the lens 42, because it is desirable to have high-beam light both below and above the horizon. In contrast, some light goes through the bottom half of low-beam lens 32, but its incidence angle is such that even when bent up by lens 32 it still turns out at or below the horizon.
As a result, there is no need in the high-beams for the step-like upward-facing reflectors used in the low-beams. Instead, the upward-facing reflectors are replaced with a bottom inward-facing high-beam reflector 106, which functions much like top inward-facing reflector 112 in reflecting light that would otherwise miss the lens 42 toward the lens 42.
The geometry is shown more clearly in
At 12 o'clock and 6 o'clock are top and bottom inward-facing reflectors 112, 106. At 3 o'clock and 9 o'clock are later inward facing high-beam reflectors 103, 109, which meet the top and bottom inward-facing reflectors 112, 106 along curves of intersection 101, 105, 107 and 111.
Note that in
It is understood that there may be variations from the specific designs shown in
Unless otherwise stated, use of the words “substantial” and “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems.
Throughout the entirety of the present disclosure, use of the articles “a” or “an” to modify a noun may be understood to be used for convenience and to include one, or more than one, of the modified noun, unless otherwise specifically stated.
Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, may be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein.
Although the methods and systems have been described relative to a specific embodiment thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, may be made by those skilled in the art.
