US1788934A - Vehicle headlight - Google Patents

Description

Jan. 13, 1931. w. H. woon v 1,788,934

' VEHICLE HEADLIGHT Filed Jan. 24, 1923 2 Sheets-Sheet 1 IN VEN TOR.

'- William H.W00d- BY ,wmmzz ATTORNEY.

Jan. 13, 1931. w. H. WOOD VEHICLE HEADLIGHT Filed Jan. 24,1923 2 Sheets-Sheet 2 FRY.

INVENTOR.

ATTOARNEY. W

Patented Jan. ,13, 1931 UNITED STATES WILLIAM H. WOOD, OF CLEVELAND, OHIO VEHICLE HEADLIGHT application filed January 24, 1923. Serial No. 614,694.

This invention relates to vehicle headlights and has for its object the provision of a simple and easily made sheet metal reflector which shall produce a legally acceptable and practically satisfactory distribution of light without the use of lenses, prisms, shades, dimmers or other expensive, fragile, or light killing devices. The present and prospec tive legislation of thedifi'erent States and municipalities requires all light rays to be kept below a certain fixed angle while affording a minimum strength of beam in other regions slightly below the horizontal, while the requirements of easy driving necessitate a restriction of the intensity at points near the vehicle in order to increase the visibility of objects at a greater distance ahead of the vehicle. These two considerations practically require a concentration of the reflected rays inside a rectangular or elliptical space whose major dimension is horizontal. addition it is desirable that the adjustment requirements be not unduly exact or sensitive, both to facilitate its use by unskilled 5 persons and to minimize the difficulty occasioned by accidental change in adjustment. A plain paraboloid reflector is inadequate to produce these results, both because of the straying of some portions of the light beam and the streaky character of otherportions, as well as the impossibility of securing this distribution except by the assistance of expensive and fragile lenses. It is possible to secure a measurably satisfactor character of light distribution by the use 0 a combination of paraboloid segments, although the focussing requirements are sometimes unduly exact and it is difficult to join the different segments in a smooth manner so as to enable easy polishing. Combinations of flat surfaces and of corrugated surfaces have also been attempted, but these are diflicult to make and are even more difficult to-repolish in case of need.

I have now discovered a new, mathematically-definite surface so located relatively to the light source as effectually to control all parts of the light beam with a hi h degree of exactness, and likewise devoid 0 all sharp angles, edges, or corrugations, thus enabling ready manufacture L and easy renovation.

Another feature of my improved surface is that the character of the light beam thrown thereby is almost entirely independent of the shape or size (within comparatively broad limits) of the light source or its longitudinal position inside the reflector.

In the drawings accompanying and forming apart of this application I have illustrated the mode of generating my improved reflector surface together with a finished reflector embodying the same. In these drawings Fig. 1 is a diagram showin the mode of generating a true parabola; Tig. 2 is a similar view showing the mode of generate in'g'my improved curve as employed for the top of my reflector; Fig. 3 shows the mode of generating the curve emplo ed for the bottom of the reflector; Fig. 4 1s a vertical sectional view of the reflector showing the relative position of the two segments; Fig. 5 is a face View of the reflector showing the mode of connecting the segments together; Fig. 6 is a View of the light pattern as thrown on a vertical, screen; Figs.- 7, 8, 9, and 10 are diagrammatic views showing the reflector segments assembled together with different relative positions of the points S and S together with the position of the light source relative-thereto.

In Fig. 1, AA is the geometrical axis,

. D-D the directrix, V the vertex, and f the focal point of theparabola A, the nature of the parabolic curve being such that every point of the same 'is equally distant from the focal point and from the directrix which is a straight line. Therefore fv=ow fb=bb fczcc fdzdd Inasmuch as no known practical source even approximates the size of a geometrical point a true paraboloid produces reflected rays of all kinds even where the source is focussed as accurately as possible; indeed a single point source if displaced from the axis will itself produce all kinds of rays since the direct rays which fall behind the parameter are converged as seeming to originate from forward of the focal point and those which impinge forward of the param-- eter are diverged as seeming to originate behind the focal point.

The essenceof my invention resides in displacing the focal point vertically from the axis and then correcting every point of the curve to compensate for this displacement. To do this I draw a line 1-1 to represent the horizontal geometrical or :n-axis and above it I located the point 8, say ,4; inch therefrom. Through this point I draw a vertical line two inches long touching the axis at 2. This line corresponds to the parameter of "a parabola and the upper end 3 of this line is a pointof the curve at which its inclination to the axis 1- -1 is exactly 45. Also at a point in the rear of the line 23 I draw a parallel line D-D', at the same distance from the point 3 as 3 is distant from 2. Thus far the procedure conforms exactly to that followed in drawing a true parabola, symmetrical about the horizontal or :v-axis with its vertex tangent to the y-axis.

I now draw an inclined line through the point S soas to intersect both the axis 11 and-the probable curve, say the line e intersecting the axis at 4. I then draw a perpendicular E E the same distance behind the line D D that4 lies in front of 2, and on the line 6 locate the point 5 which is equidistant from the line E E and the intersection 4.

I then draw another inclined line 9 through the oint S'intersecting the axis at 6, and also raw a corresponding directrix G G as far behind D D as the point 6 lies in front of the point 2. On this line 9 I then find the point 7 which is equidistant from the point 6 and from the line G G. I repeat the same performance for a suflicient number of other lines, h, 2' (etc.) to locate other points 8, 9, 10, 11 -(etc.) arid plat an accurate curve between the parameter and the vertex.

I then draw an inclined line 9' through the point S intersecting the axis at- 12 between the parameter and the vertex and to accompany it I draw a perpendicularJ J as far in front of the line D D as 12 is distant from 2, after which I find the point 13 on this line equidistant from the oint 12 and the line J J This is repeate for the lines lo and K K giving the points 14,15 and as manyother times as desired, afterwhich a curve Y is drawn connecting the points 3, 5; 7, 9, 13, 15. This curve is restricted to the re on above the line 1-1.

o secon line 20-20 as in Fig. 3 and lace at inch above it a point S from WhlCh I drop a perpendicular intersecting the axis at 21;'and on this line at about 2 inches,

' (more or less,' but preferably a little more than the distance 2-3 for a'reason to be explained hereafter) I locate the point 22 which is a pointon the curve; also below lat the line below the axis I draw a I ,point 22 shall be equidistant from 21 and from P P.

I then draw an inclined line g through the point S intersecting the axis at 23 behind the point 21 and I also draw a second perpendicular Q Q the same distance in front ofP P as 23 is behind 21. On this line I then locate the point 24 equidistant from the point 23 and from the line Q Q. After repeating this with other lines 1', t, etc. to find the points 26, 28, etc., sufiicient innumber to produce an'accurate curve, I draw other lines as u intersecting the axis at 29 in front of the point 21 and for each I draw a corresponding perpendicular as U U an equal distance behind the line P P, thus finding the points 30, 32, etc. in the same fashion; I then connect the points 22, 24, 26, 28, 30, 32 producing the curve Z.

I then rotate each curve perpendicular to its plane, the curve Y about the axis 1-1 and the curve Z about the axis 2020, to form a partial surface of revolution and I assemble these together as shown in Fig. 4 with their axes coinciding and'the points S, S spaced longitudinally apart, with the point S at the rear. If the distance 21--22 was properly chosen relative to the distance 2-3, the vertices of the two curves will match properly with the desired longitudinal separation of these pointssay inch. Also the forward end of the lower segment is slightly wider than thatof the upper segment enabling the two to be joined at the sides by wing portions X X as described and wide at the front and tapering rapidly rearwardly asthis produces a better placingof the reflected rays and also' enables, the smooth joining of the different segmentsl The heel ofthe reflector is formedJWith a socket-hole W in line with the points S, S

and the light SO lIICQ WhlCh is generally an electric light filament is located between these two points, the reflector being leaned rearwardly a slight amount so, as to elevate the axis 1-1 above the horizontal, but without elevatin the reflected rays above tlie horizontal. ration of the two points S, S. y

The lamp filament is indicated at L. In the case of the usual paraboloid reflector the effect of elevating the light source above the axis would be to cause all rays striking the reflector as if originating ahead of the parameter to be converged and those striking is compensates for the sepathe reflector as if originating behind the parameter to bediverged, thus creating an up wardly converging glare from thellower fo ralong the axis.

to spread them horizontally.

light source be located either forward of S or rearward of S and by making the distance between these at least as great as the length of the largest commercial filament a lamp is produced which ispeculiarly insensitive to focussing. Each ray of light falling on any part of the vertical zone has the same effect as though it came from a point on the axis at some distance beyond the point S, or at some nearer point within the point S, these points accordingly constituting what might be called virtual foci and these virtual foci are progressively spaced along the axis. The curve can be considered as a compound parabola wherein the foci of successive segments are progressively displaced Also this same adjustment of the curve for the vertical displacement removes sensitiveness in all other respects and further produces exactly the pattern of light beam desired, namely an oblong field, since the same correction which serves to compress the rays in a vertical plane serves Likewise every part of the field is illuminated at all times by diverging rays from one part of the reflector and by converging rays from another part thereof, thus producing a uniform, difiused illumination; and if by minor variations in the position of the lamp filament one setof rays should be weakened, the effect of another set of rays will be strengthened, thereby keeping all parts of the field illuminated to substantially the same degree unless the focussing limits be exceeded. Owing to the occurrenceof this action in three dimensions it is possible to illustrate the path of these rays only in the vertical plane since all other regions of the reflector are subjected to 'a cross fire of rays and the path of the reflected ray is seldom or never in the same plane with that of the incident ray.

It will be obvious that any light source of infinitely small size located exactly on either point S or S will have its reflected rays sent forward parallel to the axis 11 and that if it be moved to the rear of the point S all rays reflected by the segment Z will be deflected below the axis 1- 1. Likeover a considerable range of adjustment.

This same result is achieved simultaneously by the separation of the two points S and S, the light source remaining between them. and the superposed beams are deflected downwardly past the axis so that it is desirable to incline this axis upwardly to prevent the light striking the ground too near the vehicle. See Fig. 7.

It may be noted, however, that it is perfectly feasible to locate the point S ahead of the point S and compensate for the resulting upward deflection of the com ound beam by a downward inclinationof t e reflector axis as shown inFig. 8.'

Furthermore it is possible by inclining the axes of the respective portions Y and Z to obtainthe same optical results as by an axial shifting of the points S, S Thus if the lower segment be tipped downwardly as shown in Fig. 9 the same optical result is obtained as by the arrangement shown in Fig. 4, the light source being located ahead of these points. Likewise if the upper segment be tipped downwardly as shown in that in my drawings I have greatly exaggerated the elevation and separation of the points S, S as compared to the parametral radius of the curve. This particular curve is mathematically known as a cubic and when accurately made is defined by the equation wherein p represents the abcissa and c the ordinate of the point S or S; The heel portion of this curve is practically indistiguishable from the heel portion of a parabola whose focal point coincides with S or S and Whose vertex falls on the cubic and whose axis is inclined to the m-axis at an oblique angle whose abruptness increases with increase of 0 relative to 17, being zero when 0 equals zero. The points S, S exhibit many of the characteristics of a focal point.

According to another point of view the portions of the curve above the center of the reflector may be referred to the reflector axis as a modified semi-parabola in which the focal length increases from the limb toward the vertex in such a manner that all focal lines pass substantially through a selected point located above such axis, which point thus becomes the virtual focus of such curve; whilerthe portion thereof below the center of the reflector may be considered as a modified semi-parabola in which the focal length decreases from the limb toward the vertex in such a manner that all focal lines pass substantially through a selected point also located above the reflector axis. These curves, in whichever way they be" defined,

are employed as generators for defining the reflector surface, or at least that part of the same lying at and near the central longitudinal vertical plane; and conversely the reflector surface whose intersection with a verticalfaxial plane exhibits the curves herein defined contains the invention which it is my purpose to claim and secure.

- I have illustrated in detail only the type in-which the source is elevated above the geometrical, axis, but it will be apparent that the same adjustment can readily be made for a source located beneath the axis and the resulting curve built into a reflector. Such a device exhibits no advantages over the one herein illustrated and contains the defect that the two halves do not. match each other so well and are more 'diflicult to join.

, tions integrally connected together.. Such a reflector exhibits a slightly oval front but contains no corrugations, sharp angles, or reentrant' surfaces and can be plated and polished bymachine methods as easily as a plain paraboloid.

The essence of this invention resides in my new curve and the mode of compensating by theone act for; all variations en.- countered in headli ht practice, but I do not limit myself to t e particular method of laying out the curve hereii before described since the same substantial generator by whatever mathematical or drafting process it be identified falls within the purview of my invention, and I do 'notlimit myself as regards the angular extent of the generator employed or the angular extent ofthe rotation of such generator about any axis of revolution except asspecifically recited 'in my several claims. 7

Having thus described my invention what I claim is: 1

1. In a headlight, a reflector having its upper portion conforming to a surface of revolution about a substantially horizontal axis of a generator whichhas for a focus a point which is displaced above the axis of revolution, and having its lower portion also conforming to'a surface of revolution about a substantially horizontal axis of a? second generator which has for a focus a point which is displaced from the geometrical axis of said second generator, said two axes of revolution being located in the same vertical lane. 2; n a headlight, a reflector having above its central horizontal plane a surface demy signature.

fined substantially by the transverse movement of a generator which consists of a modified semi-parabola whose focal length constantly increases from its forward limb to its vertex in such a manner that all focal lines pass substantially through a selected of a modified semi-parabola whose focal length constantly decreases from its forward edge to its vertex'in such a manner thatall focal lines pass through a selected point above the parabolic axis, which point thus becomes the virtual focus of the generating curve in said vertical plane. Y

4. In a headlight, a reflector whose uppermost segment consists of a surface substantially defined by the transverse movement of a generator which consists essentially of a modified semi-parabola whose focal length increases from its forward limb toward its vertex, and whose lowermost segment consists of a surface substantially defined by the transverse movement of a different generator which consists essentially ofa modified, semi-parabola whose focal length decreases from its forward limb to ward its vertex, the focal lines of each generator passing substantially through a selected point above the corresponding parabolic axis which point thus becomes a vir tual focus for its respective generator.

5. A headlight having the portion of its reflector directly above its axis substantiallyl defined by a curve which is essentially a modified semi-parabola whose focal len h constantly increases from its forward e go toward its vertex in such a manner that all focal lines pass through a selected point above the parabolic axis, which point thus becomes the virtual focus of the curve; and having the portion of its reflector directly below its axis definedby a curve which is essentially another modified semi-parabola whose focal length decreases. constantly from its forward edge to its vertex in such a manner that all focal lines pass through a selected vpoint above such second parabolic axis which point thus becomes the virtual focus of such lower curve, both of said points and both of said virtual foci being located in the same vertical plane, a light source located above both parabolic axes and the two sides of said reflector being closed by portions whose normals all pass below said light source. 4

In testimony whereof, I hereunto afl'ix WILLIAM H. WOOD.

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