Abstract:
A condenser lens and a headlamp assembly employing the condenser lens improves control over the beam spread characteristics, while at the same time reduces the package size of the headlamp assembly. The condenser lens is provided for a projector-type headlamp assembly having a light source emitting light which is projected longitudinally downstream in front of a motor vehicle. The condenser lens generally includes a main body of light transmitting material. The main body defines a first surface receiving light from the light source and a second surface emitting the light. The second surface has at least one facet structured to spread the light and provide a predetermined beam pattern.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to motor vehicle headlamps, and more particularly relates to headlamps of the projector-type which employ a condenser lens.  
       BACKGROUND OF THE INVENTION  
       [0002]     Light emitting diodes (LED&#39;s) are fast becoming the preferable light source for automotive lighting applications, as they consume less power but provide light output which is becoming acceptable for such applications. When LED&#39;s are employed in headlamps (i.e., headlights), several requirements must be met. Specifically, the beam pattern provided in road illumination should have a certain amount of vertical spread as well as a certain amount of horizontal spread. At the same time, a vertical cut-off should be provided to minimize glare to oncoming traffic.  
         [0003]     Generally, headlamps for motor vehicles can be characterized as reflector-type headlamps or projector-type headlamps. Reflector-type headlamps employ a specially structured reflector unit which collects and redirects light from the light source, and are especially constructed to focus the light as well as provide the necessary beam spread. In projector-type headlamps, a standard projector unit employs a reflector that collects light from the LED light source and provides the beam spread. Light from the reflector passes through a condenser lens which simply and projects light from the reflector for illuminating the roadway. In a direct projector unit, no reflector is employed and a limited amount of control, is available over the beam spread through selection of the light source and its position relative to the condenser lens.  
         [0004]     The condenser lens is an imaging optic which simply projects the image placed at its focal point onto the road, thereby creating a beam pattern simply by inverting the source (left is right and up is down). These condenser lenses are aspheric lenses which are axi-symmetric and obtained by a surface revolution of a two-dimensional curve about the optic axis (i.e., a longitudinal axis extending through the lens center). To obtain control over the beam spread characteristics, the reflector of the standard projector-type headlamp is elongated, primarily in the horizontal direction, in order to obtain the desired beam spread characteristics. Desirably, the vertical beam spread is about −10° while the horizontal beam spread is about ±35°.  
         [0005]     In view of the foregoing, there exists a need to provide a projector-type headlamp which exhibits improved control over the beam spread characteristics of the outputted light.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a condenser lens and a headlamp assembly employing the condenser lens which improves control over the beam spread characteristics, while at the same time reduces the package size of the headlamp assembly. According to one embodiment, a condenser lens is provided for a projector-type headlamp assembly having a light source emitting light which is projected longitudinally downstream in front of a motor vehicle. The condenser lens generally includes a main body of light transmitting material. The main body defines a first surface receiving light from the light source and a second surface emitting the light. The second surface has at least one facet structured to spread the light and provide a predetermined beam pattern.  
         [0007]     According to more detailed aspects, the at least one facet separates the horizontal beam spread from the vertical beam spread. Preferably, the second surface has at least two facets and most preferably comprises a plurality of horizontally spaced facets extending vertically. Alternatively, the at least one facet may comprise a single facet forming the second surface and having a saddle-shape. When a plurality of horizontally spaced facets are employed, the curvature of each of the facets in the vertical direction determines the vertical spread, while the curvature of the plurality of facets in the horizontal direction determines the horizontal spread. Generally, the plurality of horizontally spaced facets forms a series of peaks and valleys on the second surface. The vertical curvatures of the plurality of facets are asymmetric relative to a horizontal axis in order to preserve the horizontal cut-off while generating the desired vertical beam spread. The facets may have either a convex curvature or a concave curvature in the horizontal direction. It will be recognized that the facets may be structured to create a predetermined beam pattern that includes regions of higher light intensity. Additionally, the cross-sectional shape of the condenser lens is no longer limited to being circular, and thus may take a square or rectangular shape to match the shape of the light emitting surface of the LED, or may take any other non-circular shape such as an oval or other oblong shapes.  
         [0008]     Another embodiment constructed in accordance with the teachings of the present invention provides a projector-type headlamp assembly for a motor vehicle which generally includes a light source, a reflector, and a condenser lens. The condenser lens is constructed in a fashion similar to the numerous constructions described above, thereby providing a predetermined beam pattern. By shifting the duties of spreading the light to the condenser lens, the reflector may comprise a simple elliptical reflector having a circular cross-sectional shape. That is, the reflector need not be elongated in the horizontal direction or otherwise specifically constructed to generate the desired beam spread pattern. A shield may also be employed in the projector-type headlamp assembly to provide a horizontal cut-off. Preferably, the shield is tilted slightly away from the light source and toward the lens thereby improving light collection. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:  
         [0010]      FIG. 1  is a perspective view of a condenser lens constructed in accordance with the teachings of the present invention;  
         [0011]      FIG. 2  is a bottom view of the condenser lens depicted in  FIG. 1 ;  
         [0012]      FIG. 3  is a side view of a headlamp assembly constructed in accordance with the teachings of the present invention and employing the condenser lens depicted in  FIG. 1 ;  
         [0013]      FIG. 3A  is a front view of a reflector and light source forming a portion of the headlamp assembly depicted in  FIG. 3 ;  
         [0014]      FIG. 4  is a perspective view of the headlamp assembly depicted in  FIG. 3 ;  
         [0015]      FIG. 5  is a schematic view depicting a beam pattern produced by the headlamp assembly of  FIG. 3 ;  
         [0016]      FIG. 6  is a perspective view of another embodiment of a condenser lens constructed in accordance with the teachings of the present invention;  
         [0017]      FIG. 7  is a bottom view of the condenser lens depicted in  FIG. 6 ;  
         [0018]      FIG. 8  is a perspective view of yet another embodiment of a condenser lens constructed in accordance with the teachings of the present invention;  
         [0019]      FIG. 9  is a side view of the condenser lens depicted in  FIG. 8 ;  
         [0020]      FIG. 10  is a perspective view of still yet another embodiment of a condenser lens constructed in accordance with the teachings of the present invention;  
         [0021]      FIG. 11  is a bottom view of the condenser lens depicted in  FIG. 10 ; and  
         [0022]      FIG. 12  is a side view of the condenser lens depicted in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Turning now to the figures,  FIGS. 1 and 2  depict a condenser lens  30  constructed in accordance with the teachings of the present invention. Notably, the condenser lens  30  is capable of imparting beam spread characteristics into the light outputted from the headlamp assembly  20  ( FIG. 3 ) of which it is a part of, as will be discussed in more detail herein below. Additionally, the condenser lens  30  is capable of creating specified vertical spread and horizontal spread functions for each facet, thereby providing a highly adaptable condenser lens which can be tailored for a specific number of vehicles or desired beam characteristics. By moving the function of beam spread from the reflector to the condenser lens, standard elliptical reflectors may be employed in conjunction with LED light sources to provide a light output that is suitable for automotive headlight applications while also having the desired beam characteristics.  
         [0024]     The condenser lens  30  generally comprises a main body  32  having a first surface  34  and a second surface  36  which are longitudinally spaced apart. The first surface  34  receives light from the light source  22  ( FIG. 3 ) and is generally planar and perpendicular to a longitudinal axis  10  ( FIG. 3 ), although it can be curved. When aligned with the center of the condenser lens  30 , the longitudinal axis  10  can also be considered the optical axis of the assembly  20 . As best seen in  FIG. 2 , the second surface  36  is formed as a plurality of facets  38 , and particularly the embodiment of  FIG. 2  includes six (6) facets although any number of facets may be readily employed. The facets  38  are generally vertically extending while being horizontally spaced apart while it is possible to have facets that are both vertically and horizontally spaced apart like a checker board design pattern. Each of the facets  38  have a generally convex curvature in the horizontal and vertical directions, and most preferably are numerically generated free form surfaces designed to provide a desired output beam. The vertical line where adjacent facets  38  meet are preferably as smooth as possible to avoid big steps between neighboring facets and depends on the nature of the particular horizontal curvatures of adjacent facets  38 . Given that each of the facets  38  may have their own horizontal curvature, a number of peaks and valleys are generally defined by the horizontal curvature of the second surface  36 .  
         [0025]     Turning now to  FIG. 3 , a headlamp assembly  20  employing the condenser lens  30  has been depicted. In addition to the condenser lens  30 , the headlamp assembly  20  generally includes a light source  22  emitting light  24  which is collected and redirected by a reflector  26 . Preferably, the light source  22  is a LED which generally produces light from a surface area, as is known in the art. The reflector  26  is preferably an elliptical reflector meaning it has an elliptical curvature as best seen from the side view of  FIG. 3 , and therefore when the LED  22  is placed at the reflector&#39;s first focal point, the reflector  26  focuses light towards its second focal point  40 , which also generally coincides with a focal point of the condenser lens  30 , as is known in the art. It will be recognized by those skilled in the art that since the condenser lens  30  will be performing all or a portion of the beam spreading function, the reflector  26  may comprise a elliptical reflector having a generally circular cross-section, as best seen in  FIG. 3A . Although an oblong or oval reflector  26  could be employed to share in a portion of the beam spreading function, the use of a circular elliptical reflector as depicted (or an oblong reflector of less width) results in a headlamp assembly  20  having reduced package size due to a reduced width (and possibly reduced height if the reflector  26  was performing some vertical beam spreading function).  
         [0026]     Returning to  FIG. 3 , the light  24  produced from the LED light source  22  is collected and focused toward the second focal point  40  where a shield  28  is positioned such that a portion of the light is redirected upwardly towards an upper half of the condenser lens  30 . Generally, the portion of the light  24  which would otherwise produce a upward beam divergence is reflected as shown, whereby most if not all of the light exiting the second surface  36  of the condenser lens  30  is directed horizontally or slightly downwardly within the preferred vertical beam spread of −10°. According to one feature of the present invention, the reflective shield  28  is preferably tilted slightly towards the condenser lens  30 , which has been found by the applicants to improve light collection by 3-15% depending upon the amount of the tilt. Specifically, the rear or upstream end of the shield  28  is tilted upwardly while the front end generally maintains its position in the vertical direction. It will also be recognized that flat or curved shields  28  of any shape may be employed and tilted as described. The shield  28  is preferably tilted by about 0° to 6° relative to the longitudinal axis  10 .  
         [0027]     It will also be recognized by those skilled in the art that the curvature of the second surface  36 , and particularly the vertical curvature as defined by the plurality of facets  36 , controls the vertical beam spread. Preferably, the vertical curvature of the second surface  36  is asymmetric relative to the longitudinal axis  10 , whereby the outputted light  24  is skewed slightly downwardly to preserve the vertical cut-off while creating the desired vertical beam spread. As such, the main body  32  includes a semi-annular surface  33  resulting from the downward end  39  of the second surface  36  being spaced further away from the first surface  34  than an upper edge of the second surface  36  is spaced away from the first surface  34  causing a prism effect. Accordingly, it will be recognized by those skilled in the art that through the use of a condenser lens  30  having a second light emitting surface  36  formed as a plurality of facets  38 , both a horizontal spread and a vertical spread can be introduced into the light beam outputted by the headlamp assembly  20 .  
         [0028]     Turning to  FIG. 4 , a schematic depiction of the headlamp assembly  20  shows the light source  22  having a rectangular shape such as would be produced by a LED light source, and which is positioned at a focal point  40  of the condenser lens  30  and relative to a vertical axis  12 , horizontal axis  14  and optical or longitudinal axis  10 . It will also be recognized by those skilled in the art that the headlamp assembly  20  could include a direct projection headlamp whereby the LED  22  would be positioned generally as shown by numeral  22  in the  FIG. 4 . In either case, the condenser lens  30  receives light at its first surface  34 , and through the construction of the second surface  36  having a plurality of facets  38 , a predetermined beam pattern  44  is produced as shown in  FIG. 5 . If a standard aspheric condenser lens (i.e., axi-symmetric) lens were employed, the lens would simply project the light source  22  placed at its focal point  40 , as indicated by the area of dotted line  42 . However, through the use of the condenser lens  30  of the present invention, a predetermined beam pattern  44  may be generated having increased horizontal spread as well as increased vertical spread. Preferably, the predetermined beam pattern  44  has a horizontal spread of ±35° while the vertical spread is about 0° to minus 10°. It will also be recognized that through the tailoring of individual facets  38 , a hot spot, say for example the area indicated by dotted line  46 , can be created. That is, each of the facets  38  may have their own unique curvature in either or both of the vertical and horizontal directions which can be structural to overlap or separate the light it outputs, thereby creating a predetermined beam spread pattern. For example, assuming the facets  38  were numbered consecutively from left to right, facets  2  and  5  could be utilized to create a particular hot spot or hot spots while the remainder of the facets could be structured to provide a more uniformly spread beam pattern. Accordingly, it will be recognized that the horizontal spread and vertical spread functions of the condenser lens  30  is separated by use of the horizontally spaced and vertically extending facets  38 .  
         [0029]     Turning now to  FIG. 6 , another embodiment of a condenser lens  130  is depicted in accordance with the teachings of the present invention. The condenser lens  130  includes a main body  132  having a first surface  134  receiving light and a second surface  136  for emitting the light longitudinally downstream in front of the vehicle to illuminate the roadway. The second surface  136  includes a plurality of facets  138 , which number three (3) in this embodiment. As best seen in  FIG. 7 , each of the facets  138  has a horizontal curvature which is generally concave in shape, unlike the convex curvature given to the facets  38  of the prior embodiment. Similar to the prior embodiment, each of the facets  138  includes a vertical curvature which is preferably asymmetric relative to the longitudinal axis or otherwise constructed to preserve the vertical cut-off while introducing a predetermined amount of vertical beam spread.  
         [0030]     Turning now to  FIGS. 8 and 9 , yet another embodiment of a condenser lens  230  is depicted in accordance with the teachings of the present invention. The condenser lens  230  generally includes a main body  232  having a first light receiving surface  234  and a second light emitting surface  236 . The second surface  236  generally is formed by a plurality of horizontally spaced and vertically extending facets  238  which function to separate the horizontal spread and vertical spread functions of the condenser lens  230 . Also similar to prior embodiments, the vertical curvature of the second surface  236  and its facets  238  is slightly asymmetric or tilted relative to a longitudinal axis to ensure the light is directed below the vertical cut-off. Thus, a lower end  239  of the lower edge  239  of the second surface  236  is spaced further away from the first surface  234  than an upper edge.  
         [0031]     Notably, it will be recognized by those skilled in the art that the embodiment of  FIGS. 8 and 9  provide a condenser lens  230  having a generally square or rectangular shape. In this manner, the condenser lens  230  may be shaped to correspond with the light source, such as an LED light source  22  which emits light from a surface such as a square or rectangular surface. As such, it will be recognized that the condenser lens  230 , and particularly as light receiving surface  234 , may take any shape, circular or non-circular, including rectangular, square, oval or other oblong shapes. In this manner, unused material of the condenser lens  230  can be eliminated, reducing the weight of the lens  230  and headlamp assembly, thereby providing a headlamp assembly which is lighter and smaller.  
         [0032]     Turning now to  FIGS. 10 and 11 , yet another embodiment of a condenser lens  330  has been depicted in accordance with the teachings of the present invention. Generally, the lens  330  includes a main body  332  having a first light receiving surface  334  and a second light emitting surface  336 . Unlike the prior embodiments, the second surface  336  includes a single facet  338  which thus itself defines the light emitting surface. In this case, the single facet  338 , (and hence second surface  336 ), has a saddle-shape which is curved in three dimensions and results in a separation of the horizontal spread and vertical spread of the predetermined beam pattern. As seen in the side view of  FIG. 11 , the main body  332  thus includes a peripheral surface  333  having a generally annular shape. It will be recognized by those skilled in the art that the single facet  338  and second surface  336  may be uniquely formed to provide any desired beam pattern and having predetermined vertical and horizontal beam spread. Preferably, the surface  336  is numerically generated to create the predetermined desired beam pattern.  
         [0033]     Accordingly, it will be recognized by those skilled in the art that the present invention provides a condenser lens and headlamp assembly which uniquely utilizes the condenser lens to provide some or all of the beam spreading function. Furthermore, this beam spreading function may be divided into its horizontal and vertical components for individualized tailoring of the outputted beam pattern. Likewise, hot spots or other desirable beam characteristics may be produced through the tailored construction of the light emitting surface and its facets. It will also be recognized by those skilled in the art that many variations could readily be employed. For example, the plurality of facets could be vertically spaced and horizontally extending, which would still result in a separation of the horizontal and vertical beam spread functions. Likewise, an unlimited number of unique single facet and multi-facet embodiments can be readily envisioned by those skilled in the art and can be tailored to specific applications.  
         [0034]     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.