Patent Publication Number: US-2002008452-A1

Title: Vehicle lamps with improved filament and filament support configurations

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application claims the benefit of provisional application Serial No. 60/044,255, filed Apr. 28, 1997. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This invention relates to lamp capsules for vehicle headlamps and, more particularly, to lamp capsules which have improved filament and filament support configurations.  
       BACKGROUND OF THE INVENTION  
       [0003] Vehicle headlamps commonly include a lamp capsule mounted in a reflector so that the light source is located at or near the focal point of the reflector. Light emitted by the lamp capsule is directed in a forward direction by the reflector. The lamp capsule typically includes a high beam filament from which light is directed horizontally in a high beam pattern and a low beam filament from which light is directed below horizontal in a low beam pattern. One of the problems involved in the design and construction of vehicle headlamps is to minimize uncontrolled light emission outside the desired beam patterns, particularly the low beam pattern, that may impair the ability of oncoming drivers to see the road and other vehicles. This uncontrolled light is known as glare.  
       [0004] The typical low beam pattern requires that little or no light be projected above the horizontal plane and requires the maximum hot spot to be projected just below the horizontal plane. Factors such as filament size and internal and external uncontrolled reflections cause the source pattern to be spread, making a sharp transition line at the horizontal plane difficult to achieve. One approach is to aim the low beam pattern slightly lower than horizontal. This reduces glare for oncoming drivers but at the expense of reducing desired illumination far down the road. Another approach is to block undesired light. However, any blockage reduces the total illumination produced by the lamp and thereby reduces the effectiveness of the lamp. There is therefore a need to improve the low beam pattern and in particular to sharpen the transition line at the horizontal plane, while minimizing the adverse impact on the total illumination.  
       [0005] In a two-filament lamp capsule, light from the low beam filament falls on the high beam filament at close range, causing it to appear as if the high beam filament were illuminated at low level in the direction of the low beam filament. Regions not facing the low beam filament remain dark. Light reflected from the high beam filament is then projected onto the reflector and into the field of view. The light reflected from the high beam filament is projected by the reflector as if the high beam filament were partially illuminated and produces a ghost image of the high beam filament. Thus, light is projected above the horizontal plane into the region that should not receive light when the low beam filament is illuminated. It is desirable to reduce or eliminate this ghost image of the high beam filament during low beam operation without substantially affecting lamp intensity during high beam operation.  
       [0006] Vehicle headlamps include a filament support structure which supports the high beam and low beam filaments in desired positions in the lamp capsule and which conducts electrical energy to the filaments. The filament support structure typically includes conductive support leads having sufficient rigidity to support the filaments under all expected environmental conditions. The filament support structure should be configured to limit blockage of light emitted by the filaments and to limit stray reflections that would adversely affect the beam pattern. Furthermore, the positions of the filaments in the lamp envelope and relative to each other have a significant impact on the beam pattern and on the overall performance and flexibility of the lamp capsule.  
       SUMMARY OF THE INVENTION  
       [0007] According to a first aspect of the invention, a lamp capsule is provided. The lamp capsule comprises a lamp envelope including a tubular portion, a dome closing one end of the tubular portion and a press seal closing the other end of the tubular portion. The lamp envelope has a central axis. First and second filaments are mounted in the lamp envelope for emitting light when energized by electrical energy. The first filament is spaced from the central axis. The second filament is mounted in spaced relation to the first filament. The first and second filaments are in a plane that passes through the central axis. The lamp capsule further comprises a support structure for supporting the first and second filaments and for supplying electrical energy through the lamp envelope to the first and second filaments.  
       [0008] The support structure preferably comprises first, second and third support leads having portions within the lamp envelope that are in the plane of the first and second filaments. Preferably, the plane of the first and second filaments and the support structure is parallel to the long dimension of the press seal. The support structure is configured to limit blockage of light emitted by the filaments and to limit stray reflections which would produce glare.  
       [0009] The first support lead may be connected to an upper filament lead of the first filament and is at least partially shadowed by the first filament when the second filament is illuminated. An upper segment of the first support lead may be angled toward the central axis to reduce stray reflections.  
       [0010] The second support lead may include a lower segment that is parallel to and spaced from the central axis and an upper segment that is bent toward the central axis and is attached to the lower filament leads of the first and second filaments between the filaments and the press seal.  
       [0011] The third support lead may include a lower segment that is parallel to and spaced from the central axis and an upper segment that is bent away from the central axis and is attached to an upper filament lead of the second filament. The upper filament lead of the second filament may be bent parallel to the central axis in the plane of the filaments and may extend toward the press seal for connection to the third support lead. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:  
     [0013]FIG. 1 is a cross-sectional side view of a vehicle headlamp assembly suitable for incorporation of the present invention;  
     [0014]FIG. 2 is an enlarged, partial cross-sectional view of the headlamp assembly, showing the lamp capsule;  
     [0015]FIG. 3 is a schematic side view of the lamp capsule and lamp base of FIG. 1;  
     [0016]FIG. 4 is a schematic bottom view of the lamp capsule and the lamp base of in FIG. 3;  
     [0017]FIG. 5 is a schematic end view of the lamp capsule, illustrating the geometry of the axial stripes;  
     [0018]FIG. 6 is a side view of an embodiment of a lamp capsule in accordance with the invention;  
     [0019]FIG. 7 is an enlarged, partial side view of the lamp capsule of FIG. 6, showing the filament support structure;  
     [0020]FIG. 8 is an end view of the filament support structure of FIG. 7;  
     [0021]FIG. 9 is a side view of another embodiment of a lamp capsule in accordance with the invention; and  
     [0022] FIGS.  10 A- 10 C are schematic end views of the lamp capsule in different rotational orientations. 
    
    
     DETAILED DESCRIPTION  
     [0023] An example of a vehicle headlamp in accordance with the invention is shown in FIGS. 1 and 2. Like elements in FIGS. 1 and 2 have the same reference numerals. A vehicle headlamp  10  includes a lamp capsule  12  mounted within a reflector  14 . A lamp base  16  mechanically mounts lamp capsule  12  in reflector  14  and supplies electrical energy to lamp capsule  12 . The open side of reflector  14  is closed by a light-transmissive cover or lens (not shown).  
     [0024] Lamp capsule  12  includes a lamp envelope  20  of a light-transmissive material, such as glass, which defines an enclosed volume  22 . A low beam filament  24  and a high beam filament  26  are mounted within lamp envelope  20 . Conductive support leads  30 ,  32  and  34  provide mechanical support for filaments  24  and  26  and supply electrical energy to filaments  24  and  26 . A lead frame  36  provides mechanical support for support leads  30 ,  32  and  34  and filaments  24  and  26 . Leads  30 ,  32  and  34  pass through a press seal  40  of lamp envelope  20  and contact conductors in lamp base  16 .  
     [0025] Lamp envelope  20  includes a generally tubular portion  42  having a central axis  44 . The tubular portion  42  is closed at one end by a tip-off portion, or dome,  50  and is closed at the other end by press seal  40 . In a preferred embodiment, dome  50  is shaped to trap light emitted by filaments  24  and  26  in the direction of dome  50  and to thereby reduce glare. A light-attenuating layer  52 , such as black paint, covers the outside surface of dome  50  and prevents transmission of light through dome  50 .  
     [0026] The reflector  14  has a reflecting surface  60  that may have one or more sections, each, for example, being a parabolic surface of revolution about an optical axis of the reflector. The lamp capsule  12  is positioned by base  16  such that filaments  24  and  26  are located at or near the focal points of the reflecting surface, and the central axis  44  of lamp envelope  20  is co-linear with the optical axis of reflector  14 . Light emitted, for example, by filament  24  is reflected by reflecting surface  60  in a forward direction through an open side of reflector  14 , as indicated by rays  62 . Light emitted by filament  24  and reflected by reflecting surface  60  is directed nearly parallel to the optical axis of reflector  14  and produces a desired beam pattern. Similarly, light emitted by filament  26  is reflected by reflecting surface  60  in a forward direction and produces a desired beam pattern. Reflecting surface  60  may have different parabolic sections and may be complex. The reflecting surface may include more than one parabolic reflector. The lamp capsule of the present invention may be used with a variety of different reflector configurations.  
     [0027] Because filaments  24  and  26  are spaced apart within lamp envelope  20  and have different positions relative to the focal point of reflecting surface  60 , they produce different beam patterns. Typically filament  24 , which is located on or near the central axis of lamp capsule  12 , is the low beam filament, and filament  26 , which is spaced from filament  24  and is displaced axially toward press seal  40  relative to filament  24 , is the high beam filament.  
     [0028] As indicated above, a partially illuminated image of the high beam filament may be produced in the beam pattern of the vehicle headlamp when the low beam filament is energized. The image, which is caused by light emitted by the low beam filament and reflected by the deenergized high beam filament, contributes to glare.  
     [0029] According to a feature of the invention, the lamp capsule  12  includes at least one light-attenuating axial stripe on the lamp envelope. An embodiment of the lamp capsule including axial stripes is illustrated in FIGS.  3 - 5 . Like elements in FIGS.  1 - 5  have the same reference numerals. In the example of FIGS.  3 - 5 , light-attenuating axial stripes  80  and  82  are provided on the outer surface of lamp envelope  20 . Axial stripes  80  and  82  are spaced apart from each other and are substantially parallel to central axis  44  of lamp envelope  20 . Axial stripes  80  and  82  preferably extend over the entire length of the tubular portion of lamp envelope  20 . The axial stripes may be any material which is substantially opaque to the light emitted by low beam filament  24  and which is compatible with the environment of the vehicle headlamp. In a preferred embodiment, the axial stripes may be black paint.  
     [0030] The axial stripes  80  and  82  are positioned and dimensioned on lamp capsule  20  so as to reduce or eliminate the ghost image of the high beam filament when the low beam filament is illuminated, while minimizing the adverse impact on total illumination. More particularly, stripes  80  and  82  are positioned and dimensioned to block light, emitted by low beam filament  24  and reflected by high beam filament  26 , which would be projected above the horizonal plane in the low beam pattern.  
     [0031] Suitable geometries of the light-attenuating axial stripes are described with reference to FIG. 5. As indicated above, at least one light-attenuating axial stripe is positioned on lamp envelope  20  to block light emitted by low beam filament  24  and reflected by high beam filament  26 . In the example of FIG. 5, axial stripes  80  and  82  are equally spaced from a plane  90  containing filaments  24  and  26 . Axial stripes  80  and  82  may be defined by angular widths relative to central axis  44  and angular spacings from plane  90 . Preferably, each axial stripe is spaced from plane  90  by an angle  94  relative to central axis  44  in a range of about 17 to 20 degrees and has an angular width  92  relative to central axis  44  in a range of about 1 to 16 degrees. In one example, angle  94  is about 18 degrees and angle  92  is about 16 degrees. It may be observed that axial stripes  80  and  82  are approximately spaced by the projected diameter of high beam filament  26  on envelope  20 . This may be understood from the fact that a region of lamp envelope  20  between axial stripes  80  and  82  is shadowed by filament  26  when filament  24  is illuminated. The widths of axial stripes  80  and  82  are selected to block light emitted by filament  24  and having grazing incidence on filament  26 . It will be understood that it is not practical to block all light emitted by filament  24  and reflected by filament  26 . In a preferred embodiment, axial stripes  80  and  82  have widths that are approximately equal to the diameter of filament  26 . The axial stripes preferably extend the entire length of the tubular portion of the lamp envelope, but may have a shorter length within the scope of the invention.  
     [0032] In one example of a lamp capsule in accordance with the invention, lamp envelope  20  has an outside diameter of 0.580 inches and filaments  24  and  26  are spaced by 2.3 millimeters. Angle  92 , representative of the width of axial stripes  80  and  82  is 16 degrees, and angle  94 , representative of one half the spacing between axial stripes  80  and  82 , is 18 degrees.  
     [0033] Tests of lamp capsules with and without light-attenuating axial stripes as described above have demonstrated that European standards for vehicle beam patterns can be achieved more easily when the axial stripes are used.  
     [0034] It will be understood that the width, position, number of stripes and length of stripes may be varied within the scope of the invention. The number of axial stripes, the length and width of each axial stripe and the position of each axial stripe on lamp envelope  20  are functions of the diameter of lamp envelope  20 , the sizes of filaments  24  and  26 , the spacing between filaments  24  and  26  and the acceptable reduction in total illumination produced by the axial stripes. The primary requirement is that one or more axial light-attenuating stripes be positioned to intercept at least a portion of the light emitted by the low beam filament and reflected from the high beam filament, with the high beam filament deenergized.  
     [0035] A further feature of the invention is described with reference to FIG. 3. Light-attenuating rings  100  and  102  are applied to the outer surface of lamp envelope  20 . Light-attenuating ring  100  is located at the lower end of tubular portion  42  of lamp envelope  20  adjacent to base  16 , and light-attenuating ring  102  is located at the upper end of tubular portion  42  adjacent to dome  50 . Rings  100  and  102  control the length of a clear zone of lamp envelope  20  through which the light from filaments  24  and  26  can pass. The filaments  24  and  26  are located relative to a base reference plane  104  in the fabrication process. One or both of rings  100  and  102  may be utilized. The rings  100  and  102  may be added relative to the base as a completion step in the calibration of the light source. A metal cap  110  that surrounds the bottom portion of the lamp capsule acts as a primary baffle, with one or two rings added if necessary as an optional trim or final calibration. The light-attenuating layer on dome  50  may be calibrated by the addition of ring  102 . The rings  100  and  102  may or may not be required, depending on the positioning of the edges of cap  110  and the coating on dome  50 .  
     [0036] The masking of the filament ends with rings  100  and  102  generates filament images that have a sudden extinction of light. This permits fabrication of intensity patterns with a higher degree of control by portions of the reflector that have little, if any, control without these boundaries on the light transmitting area. The images from the region of the reflector close to the optical axis have a high degree of magnification that distorts and enlarges the filament image. Trimming one end of the distorted image permits control of a portion of the beam to the left of the vertical axis that can be used for horizontal aim. In addition, the trimmed images can be used to position the hot spot nearer to the horizon while limiting stray light above the horizon.  
     [0037] An additional feature of the invention is described with reference to FIGS.  6 - 9 . Like elements in FIGS.  1 - 9  have the same reference numerals. A lamp capsule  190  is shown in FIGS.  6 - 8 . Low beam filament  24  is displaced from central axis  44 , typically by about 0.030 inch, to limit wall reflections. The high beam filament  26  is located in a plane defined by central axis  44  and low beam filament  24  and is displaced radially from low beam filament  24 , typically by about 0.090 inch. More specifically, each of filaments  24  and  26  typically has a helical configuration. Filament  24  has a central axis  194 , and filament  26  has a central axis  196 . The respective central axes  194  and  196  of filaments  24  and  26  and central axis  44  of lamp envelope  20  are in a plane  192  (FIG. 8) and are parallel to each other. High beam filament  26  may be displaced axially toward press seal  40 , typically by about one third of its length, with respect to low beam filament  24 .  
     [0038] A support structure for filaments  24  and  26  includes support leads  200 ,  202  and  204 , and lead frame  36 . In a preferred embodiment, the portions of support leads  200 ,  202  and  204  within lamp envelope  20  are substantially coplanar with filaments  24  and  26 . The plane  192  containing filaments  24  and  26 , and support leads  200 ,  202  and  204  is preferably parallel to the long dimension of press seal  40 , as best shown in FIG. 8. This configuration permits the lamp capsule to be rotated about low beam filament  24  for left hand drive and right hand drive applications, as described below. Furthermore, the disclosed filament and filament support structure facilitates manufacturing of the lamp capsule. The support structure for filaments  24  and  26  is configured for an improved beam pattern and reduced glare in comparison with prior art vehicle lamp capsules.  
     [0039] Each filament lead is preferably provided with a sleeve  206  of molybdenum. The sleeve  206  is attached to the filament lead by crimping and is welded to the respective support lead. Thus, where a filament lead is described as connected to a support lead, it will be understood that a sleeve is utilized.  
     [0040] Support lead  202  includes a lower segment  210  that is parallel to and spaced from central axis  44 . An upper segment  212  of support lead  202  is bent in the plane of filaments  24  and  26  toward press seal  40 , and is connected to the lower ends of filaments  24  and  26 . Support lead  200  includes a lower segment  220  that is parallel to and spaced from central axis  44 , and an upper segment  222  that is angled toward central axis  44  in the plane of filaments  24  and  26 . The upper segment  222  of support lead  200  is connected to filament lead  224  near the upper end of low beam filament  24 . Preferably, filament lead  224  is nearly perpendicular to central axis  44 . The angle of upper segment  222  of support lead  200 , typically about 15° to 20°, is selected so that light emitted by low beam filament  24  is reflected downwardly by upper segment  222  when the lamp capsule is mounted in a vehicle lamp reflector. Because support lead  200  is located in the plane of filaments  24  and  26 , support lead  200  is at least partially shadowed by filament  24  when high beam filament  26  is illuminated.  
     [0041] Support lead  204  includes a lower segment  230  that is parallel to and spaced from central axis  44 , and an upper segment  232  that is bent away from central axis  44  in the plane of filaments  24  and  26 . Upper portion  232  of support lead  204  is connected to filament lead  234  from the upper end of high beam filament  26 . In the embodiment of FIGS.  6 - 8 , filament lead  234  is bent toward press seal  40 , and includes a section that is substantially parallel to central axis  44 . The connection between filament lead  234  and the upper portion  232  of support lead  204  is made below filament  26  in a region between filament  26  and press seal  40 . Filament lead  234  is preferably in the plane of filaments  24  and  26 , and is at least partially shadowed by filament  26  when low beam filament  24  is illuminated. In addition, it may be observed that the support leads  202  and  204  for filament  26  are located in the region between filament  24  and press seal  40  and have minimal impact on light emitted by filaments  24  and  26 . In general, support leads  200 ,  202  and  204  are configured to limit blockage of light emitted by filaments  24  and  26  and to limit stray reflections which would produce glare.  
     [0042] An alternate embodiment of the filament support structure is shown in FIG. 9. Like elements in FIGS.  6 - 9  have the same reference numerals. The embodiment of FIG. 9 differs from the embodiment of FIGS.  6 - 8  primarily with respect to the support lead for the upper end of high beam filament  26 . A support lead  250  includes a lower segment  252  parallel to and spaced from central axis  44 , and an upper segment  254  parallel to central axis  44 , but displaced outwardly in the plane of filaments  24  and  26  with respect to lower segment  252 . Segments  252  and  254  are connected by an intermediate segment  256  disposed between filament  26  and press seal  40 . An upper end of segment  254  may be bent inwardly and connected to a filament lead  260  of filament  26 . Filament lead  260  may extend upwardly at an angle with respect to central axis  44 . The segments of support lead  250  are in the plane of filaments  24  and  26 . Upper segment  254  is shadowed by filament  26  when low beam filament  24  is illuminated, thus limiting light blockage and stray reflections.  
     [0043] Schematic diagrams illustrating various orientations of the lamp capsule of the present invention are shown in FIGS.  10 A- 10 C. Like elements in FIGS.  1 - 10 C have the same reference numerals. FIGS.  10 A- 10 C represent the lamp capsule as viewed along the central axis  44  of lamp envelope  20 . In FIG. 10A, plane  192 , which contains filaments  24  and  26  and is parallel to the plane of press seal  40 , is oriented vertically. Axial stripes  80  and  82  are spaced from plane  90 , as described above. In FIG. 10B, the lamp capsule is rotated by approximately 45 degrees in a clockwise direction about filament  24  with respect to the orientation of FIG. 10A. The orientation of FIG. 10B is used in a left hand driving vehicle headlamp. Axial stripe  80  reduces glare and provides a sharper transition at the upper boundary of the low beam pattern, as described above. In FIG. 10C, the lamp capsule is rotated approximately 45 degrees in a counterclockwise direction about filament  24  with respect to the orientation of FIG. 10A. The orientation of FIG. 10C is utilized in a right hand driving vehicle headlamp. Axial stripe  82  reduces glare and provides a sharper transition at the upper boundary of the low beam pattern, as described above.  
     [0044] It will be understood that the features of the lamp capsule described herein, including the use of one or more axial stripes on the lamp envelope, the use of one or more light-attenuating rings on the lamp envelope, and the filament support structure shown in FIGS.  6 - 9  and described above, may be used separately or in any combination to provide lamp capsules with improved beam patterns and ease of manufacture.  
     [0045] While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.