US2219848A - Optical system for dual-beam automobile headlights - Google Patents

Description

Oct. 29, 1 40- H. A. H. J. SCHAFFNER 2,

OPTICAL SYSTEM FOR DUAL-BEAM AUTOMOBILE HEADLIGHTS filed May. 4, 1958 3 Sheets-Sheet l 1940- H. A. H. J. SCHAFFNER 2,219,848

. OPTICAL SYSTEI FOR DUAL-BEAM AUTOMOBILE HEADLIGHTS 3 Sheets-Sheet 2 Filed llay 4, 1938 Patented Oct. 29, 1940 UNITED STATES OPTICAL S YSTEM FOR DUAL-BEAM AUTO- MOBILE HEADLIGHTS Henri Alexandre Hippolyte Joseph Schaflner, Paris, France Application May 4, 1938, Serial No. 206,081

* V .In France May 8, 1987 10 Claims. (Cl. 240-413) The present invention relates to optical systems for dual-beam automobile headlights. In my U. S. Patent No. 2,112,411 I have already described a dual-beam automobile headlight comprising a concave reflector, an incandescent lamp with a transverse courtesy filament and a road" filament which are located consecutively between the focus of the central anastigmatic zone of the reflector and the vertex of the latter,

the road filament being the nearest to said vertex, a cup or shield arranged below the "courtesy filament, and a convergent lens supplied with light rays by the reflector and formed with an annular marginal zone comprising circular concentric steps and fed by the unshielded road filament, and a central zone limited by a substantially semi-circular contour, provided with vertical steps and fed by the shielded courtesy" filament.

2 The semi-circular central courtesy" light portion of the outlet lens of the headlamp is provided with vertical steps for the following reason: as the steps of circular shape which receive a divergent beam play the part, adjacent the vertical axis of symmetry of the lens, of prisms which deviate upwardly the rays they receive, said steps would produce, for courtesy? illumination, an undesirable brightness above the plane of cut off, so that it has been necessary, in order to reduce to a certain extent the thickness of the central "courtesy" illumination zoneoi' the lens, to provide the latter with vertical steps forming prisms which deviate sideways the beam they receive and thus a lateral spreading effect which cannot be harmful.

However, the arrangement oi" vertical steps in said central zone does not enable the thickness of the lens to be reduced to the same extent as in its outer annular portion provided with circular steps, and an extra thickness is produced in the centre which renders the manufacture oi said lens by moulding very diflicultowing to the difl'erence of temperature in the glass caused by such differences of thickness.

According to an improvement which is the object of the present invention, this drawback is eliminated by the fact that the optical centre of the central zone which is supplied by the courtesy filament is arranged above the optical axis of the annular road light zone so that the vertical axial section of the said courtesy light zone is substantially symmetrical relatively to its optical centre, whereas the courtesy filament is raised relatively to the optical axis of the annular road zone of the lens so as to correct the upward deviation of the courtesybeam caused by the upward displacement of the optical centre of the corresponding zone of the lens and produce a downwardly turned courtesy beam. I

This arrangement further enables the portion 5 of the lens which is used for courtesy lighting to be correctly centered in respect to the portion used for road lighting, which is very important for headlights having a small diameter wherein the surface of the annular marginal portion of 10 the lens used for road lighting is considerably reduced. It is also very important in this latter 'case that the distribution of light over the surface of said marginal portion of the lens be very carefully determined, and it is another object 15 oithe invention to provide a road filament which is arranged in order to supply a relatively low light-intensity to the central portion of the lens anda very strong light-intensity to the annular portion .used for road or distant lighting. '20

In the accompanying drawings:

Figure 1 is a diagrammatical view showing in sectional elevation the device according to my previous patent. 1

Fig. 2 isa similar view with the structure mod- 25 ified to accord with the present invention.

Fig. 3 is a'view like Fig. 1 but showing a practical constructional form of the subject of the invention.

Figures 4, 5 and 6 are respectively a front view, a sectional elevation view and a horizontal section view illustrating another embodiment o1 thelens shown in Fig. 3.

Figure 17 is a perspective view (with parts broken away) of a bulb for automobile head lamp and showing the arrangement of the filaments and reflector of the structure illustrated in Fig. 3.

Figs. 8, 9 and 10 are elevations respectively of alternative arrangements of the "road" or distant lighting filament. 40

Fig. 11 is an elevational section of a lens, bulb and reflector according to the invention and showing the diagram of Fig. 3 with the lens illus-' trated in'Figs. 4, 5 and 6.

Fig. 1 shows diagrammatically an optical sys- 45 tem for a dual-beam headlamp similar to that described in my said previous patent, and comprising a spherical reflector I and a stepped lens 2 having a central zone 3 with vertical steps which is supplied by the beam emanating from the courtesy filament 4 which is arranged in a cup 5, and an outer annular zone 6 supplied by the beam emanating from the road light filament I. In order to turn the courtesy beam 7 slightly downwards, the courtesy filament 4 is ar- 55 ranged somewhat above the optical axis :s'z which will be assumed to be common to the road light and courtesy light zones of the lens, and the marginal plane of the cup I is inclined so as to pass through the centre c of the spherical reflector, the virtual image, which plays the part of the source, of the courtesy filament, and which is produced by the central anastigmatic zone of the reflector i, being formed at S in the focal plane P: of the central zone 3 of the lens 2. The direction of the downwardly turned courtesy beam. is defined under these conditions by the straight line SO connecting the image 8, which plays the part of the source, of the filament l, to the optical center of the courtesy light zone 3 of the lens. As the courtesy beam is cut off by the cup of which the marginal plane passes through the centre of the spherical reflector I, it will suillce to give the portion occupied on the lens 2 by the courtesy light zone 3 a substantially semi-circular surface, so that said courtesy zone is formed substantially by a half lens which only extends very slightly below its optical centre O to the extent necessary for compensating the turning down of the beam which supplies it. As mentioned above, said central courtesy light portion 3 of the lens is substantially thicker than it would have been if it 'had been possible to provide it with circular steps like the road light zone 6. The means which enables this thickness of glass in the zone 3 to be reduced is based on the following remark:

Assuming a piano-convex convergent lens having a given focal length. If it is desired to cut away said lens and give it a semi-circular contour, it will immediately be seen that ha height h is given (Fig. 1) for the cutaway lens, the

latter will have a minimum thickness when its vertical section is symmetrical relatively to the optical axis. This remark will enable it to be understood that to decrease the thickness of the central courtesy light zone 3 of the lens 2 of an optical system such as that shown in Fig.

1, it sufiices, as shown in Fig. 2, to displace the optical axis of said zone upwards to 1111' so that it is located substantially above the optical axis 2:: of the road light zone of the lens and for said courtesy light zone 3 to be almost symmetrical relatively to its new opticalcentre'Of. It will however be understood that the simple up-' ward displacement of the optical axis of the courtesy zone 3 of the lens will produce an upward deviation of the courtesy beam, decreasing or completely offsetting the necessary downward deviation. As a remedy for this consequence of .the displacement of the optical axis of the courtesy light zone 3 of the.lens, the invention provides for likewise displacing the courtesy light filament 4 upwards to a point 4' (Fig.2) so chosen that its image 8' is displaced upwardly relatively to the former image 8 (Fig. 1) through a distance substantially equal to the upward displacement of the optical axis 11' of the courtesy lens. It is obvious that under these conditions, the new direction S'O' of the courtesy beam will beturned downwards and substantially parallel with its initial direction 80. Of course, the cup of the courtesy filament will come into a position 3' which is more forwardly inclined so that its marginal plane still passes through the centre c of the spherical reflector i.

In the drawings, the slope of the cup has been exaggerated to clearly'show the-direction in which the source is moved, but it is obvious that in reality the marginal plane of said cup amaess must intersect the lens in the courtesy light zone 3, adjacent the lower edge of said zone.

By examining the lens 2 modified as just described and illustrated in Fig. 2, it will be seen that the fact of making the courtesy light zone 3 substantially symmetrical relatively to its axis 11' by displacing the latter upwards relatively to the optical and geometrical axis 22's: of the annular road light zone 3 leads to the creation of a discontinuity 3 on the outer surface of the lens 2 along the lower edge of the courtesy light zone 3. Said discontinuity 3 causes undesirable harmful brilliancy and hinders the manufacture of thelens by moulding; consequently the invention provides a means for raising the optical axis of the courtesy light zone while eliminating the said discontinuity, said means consisting in inclining the courtesy light zone 3 rearwardly (Fig. 3) relatively to the annular zone 3, that is to say in tilting' it about its upper edge in a clockwise direction, so as to permit of a suitable junction of the two road light and courtesy light zones of the lens. ing of the courtesy light zone 3 of the lens I obviously causes an elevation of its optical centre 0', thereby enabling the thickness of said zone to be decreased, as in the case of Fig. 2. The upward-deviation of the courtesy beam ,which ensues therefrom (the inclined lens is equivalent to a piano-convex lens placed against an elevating prism having its base at the top) is corrected as previously by raising the courtesy filament to 4. The rearward tilt of the courtesy light zone 3 of the lens furthermore causes a slight transverse aberration which advantageously increases the horizontal spread of the courtesy beam.

The best result will be'obtained when the vertical axial section of the courtesy light zone 3 is symmetrical relatively to its optical axis y'u which is rearwardly inclined owing to the above-mentioned tilting, and when the centre of curvature of the outer spherical face of said courtesy light zone 3 is at 8 on the optical axis of the annular road light zone 3 of the lens 2.

As mentioned above, the road light filament l is arranged on the axis :c'a: and to the rear of the courtesy filament 4 so as to supply the reflector I with a more divergent beam than the beam emanating from the courtesy filament. in order to cover the whole surface of the lens 2. It ensues that the focal length of the annular road light zone 3 must be smaller than that of the courtesy light zone. Now, the radii of curveture of the outer spherical face and of the inner steps of the annular road light zone 3 are determined by considerations of bulk and of efflciency which most often lead to a bi-convex lens. on the other hand. it is convenientto take a piano-convex lens for the central courtesy light zone 3, the plane face being divided into parallel vertical steps which can be made by simply milling the mould. Under these conditions, the adjustment of the focal length of the courtesy light zone 3 relatively to the focal length of the road light zone 3 will be effected by acting on the outer face of the courtesy light zone which will most often have a greater curvature than that of the annular road light zone (Figs. Said central zone 3 which is limited by a flattened semi-circular contour III, will in this case have an outer surface of revolution about a vertical axis. However, to enable the mould necessary for the manufacture of a lens of this kind having two different curvatures to This rearward tiltbe more readily and more accurately made on a lathe, said lens will preferably have a central of the road light zone 8, will be corrected by acting on the convexity of the circular steps provided on the rear face of said zones l2, l2 in such a manner as to give them suitable focal lengths for the road light. I

The vertical steps ii of the central courtesy light zone 8 will preferably have a horizontal cross-section of curvilinear shape (Fig. 6), for example circular, thereby permitting the elimination of the vertical shadows produced in the courtesy beam by the junctions of the plane faced vertical steps, by virtue of the conicity of therefiected beam which supplies them.

Another object of the present invention is to improve the road beam or unshielded beam produced by a dual-beam automobile headlamp of the above described type. It is known that the road beam of an automobile projector should have a horizontal opening which is greater than its vertical opening so as to illuminate the side plaths and side approaches of the road. As, furthermore, a luminous beam making a given angle with the optical axis impinges on the objects to .be

illuminated located in planes adjacent the horizontal plane, at a greater distance than in all the other planes, the curves of equal illumination, called "isolux'f curves, which are located in a plane perpendicular to the optical axis of the projector, must have a horizontally elongated shape if it is desired to obtain a constant illumination throughout the whole-field. It is known, on the other hand, that the illumination at a point of the field is proportional, leaving out of account the coefllcient of transmission of the reflector and of the lens, to the surface of the projector which is seen illuminated from said point, and it can be readily shown that for a given optical system, the apparent illuminated surface of the projector, seen from a point of the field, increases with the mean value of the opening of the elementary luminous cones issuing from said surface, that is to say with the mean value of the solid angle at which the source is seen from the zone of the reflector used for illuminating the part of the field in question. To fulfill these conditions, a horizontally elongated reflector can be used the shape of which is so determined that the zones of the lens which are used for illuminating the parts of the field adjacent the horizontal plane passing through the optical axis, receive a maximum illumination, which amounts to given the elementary luminous cones issuing from said zones maximum opening. However, for reasons of convenience of construction and to increase the area of the anastigmatic central zone of the reflector, one is led to use, as mentioned above, a spherical reflector preferably formed by a silvered portion of the wall of the lamp, and of which the silvered surface is more enveloping horizontally than vertically. This arrangement gives the beam a horizontal opening which is greater than its vertical opening, without however transversely elongating the isolux curves.

According to the invention, the elongation in the transverse direction of the curves of equal illumination given for road lighting by a projector of this type, is obtained by the fact that the lamp has a road filament of which the axis of svmand a road filament metry is arranged in the vertical plane passing through the optical axis of the system and that it is substantially perpendicular to said optical axis. It will be understood that by means of this arrangement, the road filament is seen at a greatv solid angle from the side zones of the reflector which supply the marginal annular zone of the lens and which act widthwise, and this is contrary to what takes place in the case of the transverse horizontal arrangement of the road light filament wherein said filament is seen endwise from the' side zones of the reflector, therefore at small solid angle, the axis of the filament thus forming a direction of minimum intensity. owing to the anastigmatism of the central zone of the reflector, this vertical arrangement of the filament enables a satisfactory vertical opening to be obtained without producing a more luminous patch on the ground, which impairs the evenness of the illumination, as would be the case in the usual projectors having a parabolic reflector.

I Finally, the central zone which is used for distant lighting is still supplied by the vertical filament since the latter is likewise seen from said zone at a great solid angle, so that the axial power of the beam is excellent, contrary to what occurs in the case of the axial horizontal arrangement of the road light filament wherein said filament is seen from the central zone of the reflector by one of its ends.

Referring to Fig. 7 it is seen that the spherical shaped lamp 2| which is provided with a horizontally enveloping silver coat and of which only the contour 22 has been shown, contains a transverse courtesyfilament 23 arranged in a cup 24 25 formed by two helically wound arms arranged vertically one behind the other and to the rear of the courtesy filament 23, the assembly of the filament and'the cup being supported by rearwardly inclined supports 26, 26,

26 held in the base 21 of the lamp, in such a manner that the filaments are placed between the wall of the reflector and the focus of its anastigmatic top zone. By way of an indication, it can 9), or again by two coils 325 arranged in a trans-- verse vertical plane perpendicular to the vertical plane passing through the optical axis, said coils being vertical or slightly inclined relatively to said Furthermore,

axial vertical plane (Figure 10), the axis of symmetry of the filament as a whole being always contained in said plane. In the vertical direction said filament is arranged symmetrically relatively to the optical axis of the projector, or preferably slightly lowered so that about two thirds of its length are located below said optical axis, thereby avoiding, owing to the anastigmatism of the zone of the mirror that acts for distance lighting, the production on the ground at a short distance from the projector, of a violently illuminated central patch which produces a harmful contrast eilect.

, Furthermore, by somewhat lowering the road filament 25, it can be arranged so that its upper end does'not exceed in height the rear horizontal edge of the courtesy light cup, thereby preventing the two filaments from mutually illuminating each I as Just been described enables, in combination with the optical system having two elements viz: a reflector and a rei'ractor, hereinbei'ore described, a beam to be obtained which has the desired horizontal and vertical opening and distribution so 7 that it is not necessary to have recourse to horizontal or vertical dispersion members which decrease the axial intensity and therefore the range.

Furthermore, this vertical arrangement oi the road filament inv a projector according to the invention enables the space between the axis of maximum intensity of the road beam and the horizontal cut-off plane of the courtesy beam to be made practically independent of the vertical distance between the'two filaments, on the sole condition that the vertical road filament intersects the optical axis: said space will only depend in practice on the relative position of the road light and courtesy light lenses which are madeintegral by moulding, so that the adjustment or the courtesy beam relatively to. the road beam can only vary in a quite insignificant manner from one headlamp to the other.

What I claim is: v

1. An optical system for dual-beam automobile headlights comprising a concave reflector, a lamp with a shielded "courtesy" filament and an inshielded road filament located consecutively between the iocus of the central anastismatic zone of the reflector and the vertex of the latter, a convergent lens supplied with light rays by the reflector, and iprmed with an annular marginal zone comprising circular concentric steps supplied with light by the unshielded "road" filament, said lens having a central zone limited at its upper portion by a substantially semi-circular contour and provided with vertical steps and supplied with light by the shielded "courtesy filament, said central zone having, in diametrical vertical section, its optical center approximately in the middle of its height, said central zone having approximately the same thickness at its upper portion and at its lower portion as .the regions or the annular "road" zone with which said portions merge, the said optical-center of said central zone being above the optical axis of the annular "road" 7 zone, and the said central zone being inclined 10rwardly and merging, without projection, with the annular zone, the said "road filament being arranged above the said optical axis of the annular zone.

2. An optical system according to claim 1, wherein the axis of symmetry of the road filament is arranged in a vertical plane passing 5 through the optical axis of the system, said filament being substantially perpendicular to said optical axis.

3. An. optical system according to claim 1, wherein the road filament comprises a coil havini' a vertical axis.

4. An optical system according to claim 1. wherein the road filament comprises two vertical coils connected in series and arranged one behind the other.

5. An optical system according to claim 1, wherein the road filament comprises 'two coils arranged one behind the other in a vertical plane passing through the optical axis of the system and slightly inclined in that plane to form a V.

6. An optical system according to claim .1, wherein the road filament comprises two coils arranged in the form of a V in a transverse vertical plane perpendicular to the optical axis or the system.

7. An optical system according to claim 1, wherein the road filament is arranged vertically substantially symmetrically relatively to the optical axis oi the system.

8. An optical system according to claim 1, wherein the axis of symmetry 01 the road filament is arranged in a vertical plane passing through the optical axis of the system, said filament having about two thirds of its length below said optical axis. a

9. An optical system according to claim 1, wherein a shielding cup is arranged below the courtesy filament, the unshielded road filament being so arranged that its upper end does not extend beyond the rear horizontal edge of said cup.

10. An optical system as claimed in claim 1, in which the central zone of the front surface of the. lens has a smaller radius oi! curvature than that of the annular marginal zone, said central zone being of an area to include some or the inner concentric circular steps of the annular "road" zone, said concentric steps having inner convex surfaces, the. curvature oi. the inner circular steps included in said central zone being different from the curvature of the outer circular steps to compensate for the increase of curvature oi! the outer surface of the lens opposite said inner circular steps.

HENRI ALEXANDRE HIPPOLYTE JOSEPH SCI-IAFFNER'.

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