US2302979A - Vehicle headlight - Google Patents

Description

Nov. l24,v 1942- J. J. SHERIDAN Erm. 2,302,979

vlsmlma HEAD LIGHT Filed Jan.. 21. 1941v z'sheets-sheet 1 Nav. 24, 1942, J, J; SHERIDAN E; Ag f 2,302,979

VEHICLE HEAD LIGHT Filed Jan. 21. 1941 2 sheets-sheet 2' INVENTQRS J.J. Sher' dan W.A.H ornng D.L.Dearborn Patented Nov. 24, 1942 UNITED STATES PATENT OFFICE VEHICLE HEADLIGHT Joseph J. Sheridan, San

Mateo, Robert L.

Application January 21, 1941, Serial No. 375,298

2 Claims.

This invention relates to improvements in Vehicle headlights and more particularly to a reflector designed to give a downwardly directed illumination.

Our invention comprises a reector having a contour which is so shaped and positioned with respect to a light source of known iinite size and shape, that the luminous flux is distributed in a vertical. plane in accordance with a predetermined illuminated pattern wherein there are substantially no light rays directed thereabove. A reflector made in accordance with our invention is particularly adapted to direct light rays so there is substantially no glare in the eyes of motorists who in the normal course of driving are proceeding vin the opposite direction.

In order that objects above the level of the surface of the highway be visible, it is necessary that a small part of the light flux be directed above a horizontal plane intersecting the Vertex of the reflector. By having this upwardly directed part of the light flux also directed substantially to the right there is no glare in the eyes of persons proceeding normally in the opposite direction, and still the requirements as to the illumination of objects above the horizontal are satised. Upwardly directed rays must be accurately controlled to avoid glare and there must be no uncontrolled, aberrant rays which, in causing glare, constitute a negative factor in visibility, thereby reducing the effectiveness of the illumination aiorded by the headlights.

These results are attained by designing a reilector, not paraboloidal, but one embodying that perturbation from a paraboloid capable of reflecting the light rays from a light source of nite size and shape so as tc produce the lumen distribution in the emitted light beam fullling predetermined calculations and legal requirements for visibility.

Our invention will be better understood from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a table showing the horizontal and vertical candlepower distribution of light ilux on an illuminated pattern as a typical requirement; Fig` 2 is a graph showing relative light flux distribution with respect to a dihedral angle. Curve I represents the ideal requirement for flux distribution with respect to dihedral angle a; curve II represents the flux distribution of a true paraboloid wherein the light source is located about one and one-half inches from the vertex of the paraboloid and all of the source is located above the focal point of the paraboloid (Cl. 24U-41.35)

and in the Y-Z plane; and curve III represents the light ux distribution from a reector embodying our invention, the contour of which differs from a true paraboloid by a calculated amount constituting the perturbation therefrom, and which perturbated paraboloid has its light source located approximately three inches from the Vertex V, all of said light source being positioned in a plane passing through the axis Y-Y and Z-Z and above the focal point So;

Fig. 3 is a diagrammatic illustration showing a reflector embodying the principles of our invention in Vertical section, the curvature of said reflector being shown in full lines and that of a true paraboloid being shown by a single line, there being also shown certain geometrical principles on which our device is based;

Fig. 4 is a front view of the reflector embodying the principles of our invention, there being also shown certain geometrical principles on which our device is based; and

Fig. 5 is a vertical section taken through a reflector embodying our invention, showing by the dotted lines a true paraboloid.

There are ve factors which are considered as being basic in the development of a formula for a reflector contour embodying the principles of our invention, namely: (a) That the light source or filament of the headlamp be not a point, but one of definite and known size and shape; (bi) when considering the requirement as to ilux distribution on an illuminated pattern that the light source of denite and known size and shape be positioned at a predetermined distance from the vertex of the reilector; (c) with the size, shape and position of the light source being known, as well as the requirement as to ilux distribution on an illuminated pattern, that the amount of perturbation of the reilector from a true paraboloid be such as to satisfy the said requirements as to ilux distribution; (d) that the light source be shielded so no rays can emanate outwardly from it in a direction above the horizontal; and (e) that the vertical angle subtended by the light source at the vertex or at the point on the reflector contour nearest to the said source, shall not exceed two degrees when the vertical angle subtended by the principal part of the illuminated field is four degrees; or, in other words, that this ratio shall be:

angle 1:1@ angle a Since the design of the contour of the reflector surface is dependent primarily upon the vertical distribution of the luminous flux at the illuminated pattern, it is essential that said distribution be determined at the outset. A distribution, typical of such a requirement is shown in Fig. 1, which shows horizontal angle as well as vertical angle candlepower distribution. Curve I shown on Fig. 2 is derived from the said table of Fig. l by computing lumen distribution in each vertical angle zone from the candlepower distribution in each corresponding vertical angle zone. Curve I, therefore, provides one basis upon which the reflector contour will be designed.

The requirement as to distribution of light flux on the illuminated pattern is illustrated graphically by Fig. 2 in which the ordinate is in relative luminous flux per degree of dihedral angle and the abscissa is in degrees of dihedral angle. This dihedral angle is defined as the angle between the horizontal plane through the focal point of the reflector and any plane through the Z axis.

A true paraboloid in which the source is one and one-half inches or less from the vertex,vor subtends an angle at the vertex of four degrees or more will give rise to the flux distribution shown by curve II, approximately, providing all of the source be above the focal point.

This large deviation from the requirement indicated by curve I, we pr'opose to eliminate by increasing the distance from the source to the reilector vertex and by changing the shape of the reflector contour by a certain calculated amount, thus producing the flux distribution curve III, and very closely approximating the required curve I.

To satisfy this requirement and produce curve III, the calculation of the amount by which our reflector contour differs from the contour of a true paraboloid will be explained in terms of the symbols of Fig. 3. In this figure, X-X is the axis of the reflector and is a horizontal line through the focus and the vertex of the true paraboloid with which the calculation starts; Y-Y is a vertical line through this focus; P is the contour of the true paraboloid; V is the vertex of the true paraboloid; R is the contour of the perturbed paraboloid producing the flux distribution of curve III, Fig. 2; p is the difference in the radius vector of the true paraboloid and that of the perturbed paraboloid; is the angle between the X axis and a typical ray from a point on the source; N is the point of incidence of this ray on the reflector contour; NN is the reflected ray; NA is a line parallel to the X axis; a is the angle between the X axis and the projection on the XY plane of NN; d is the angle subtended at V by the source S; S0 and Sn are the extreme points of the source in a vertical plane.

The quantity, p, the perturbation which must be added to the true paraboloid in order to produce the required reflector contour is obtained by expressing it as a power series in 0 or of angle a with unknown coefcients; by substituting in the formula for flux distribution due to a single point of the source; integrating over the source; equating the result to the required function of angle a shown by curve I, Fig. 2. This last step fixes the values of the unknown coefficients and makes p a known function of 6.

For the numerical requirements shown by curve I, and for the distance V-SO equal to three inches, or angle d equal to 2, and for all of the source located above S0, in Figs. 3 and 4, the perturbation, p, equals 0.011 02 inch, with angle 0 expressed in radians.

r is the radius vector of paraboloid P. The

radius vector of the reiiector Ris r-HJ. The light shield is designated by the numeral 6.

To the open face of the reflector must be added a v cover glass having certain optical properties.

'By means of vertical flutes, or cylindrical lenses,

properly designed for use with the reflector above described, the vertical or dihedral angle flux distribution can be redistributed horizontally on the illuminated pattern in any desired relative density necessary to satisfy the existing laws, regulations or other requirements determined from practical needs for the device.

As an example, we have described our invention as being particularly useful as a vehicle headlight. It is apparent, however, that the principles of our invention are equally applicable to searchlights, oodlights or lamps of various kinds, so for this and other obvious reasons it is to be understood that our invention is to be broadly included within the scope of the appended claims.

Having described our invention, what we claim l. In a light projector, the combination comprising a light source of predetermined size and shape, a reflector positioned to reflect light rays emanating from said source, said reflector being so positioned with respect to said source that the angle subtended by said source at the Vertex of the reflector is substantially two degrees, the said source being located at and above the focal point of the reflector, the said reector having an effective surface which is generated by the revolution of a curve that varies from a true paraboloid by a certain perturbation, the said perturbation being determined by the use of the coordinate formula p=(0.011iC) 62 in which p is given in decimals of an inch and 0 is given in radians between the limits of zero and pi over two and C has a value greater than zero and less than 0.011, and means for preventing the emanation of light rays upwardly and forwardly.

2. In a light projector, the combination comprising a light source of predetermined size and shape, a reflector positioned to reflect light rays emanating from said source, said reflector being so positioned with respect to said source that the angle subtended by said source at the vertex of the reflector is substantially two degrees, the said source being located at and above the focal point of the reflector, the said reflector having an effective surface which is generated by the revolution of a curve that varies from a true paraboloid by the perturbation p thereof, and which curve is determined by use of the polar coordinate formula 6 mtr-.awww

in which r is the radius vector in inches, 0 is the polar angle in radians and varies between radians, 7c is one when the latus vectum equals twelve inches and varies directly with the latus vectum, p equals 0.011 02, inches.

f zero and pi over two JOSEPH J. SHERIDAN. ROBERT L. DEARBORN. WENDELL A. HORNING.

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