Claims
- 1. A dipped headlamp for motor vehicles comprising a bulb and a reflector having a reference axis and a closure glass placed in front of the bulb ad the eflector, and adapted to create a light beam under a cut-off defined in a standardized vertical transverse screen by two horizontal half-lines at different heights, and on the opposite sides of a vertical center line, the left-hand half-line being at the lower level;
- said bulb being an axial filament bulb with its light-emitting surface completely exposed,
- said reflector comprising a reflecting surface without any discontinuity and forming on said screen images of the filament such that substantially all points of said images are below a horizontal line contained in said screen and intersecting the reflector axis, and the side portions of the reflector forming images of the filament smaller than the center portion thereof,
- the axis of the filament and the axis of the reflector being both inclined downwardly with respect to the horizontal in such manner that said horizontal line is at the same level as the lower half-line of the cut-off,
- the axis of the filament and the axis of the reflector being further inclined to the right at an angle corresponding to about one half of the horizontal extent of said concentration images, and
- the headlamp further comprising correction means associated with said side portions of said reflector for angularly displacing said concentration images upwardly to the level of the right-hand upper half-line.
- 2. A headlamp according to claim 1 wherein said upper half-line is at the level of a horizontal headlamp axis and the lower half-line is tilted below said horizontal headlamp axis by about 1.5%.
- 3. A headlamp according to claim 1 wherein the correction means comprise said side portions of the reflector being upwardly tilted relative to the remainder of the reflector, the closure glass being substantially smooth.
- 4. A headlamp according to claim 1 wherein said filament images formed by the reflector each have their highest point substantially on said horizontal line intersecting the reflector axis.
- 5. A headlamp according to claim 4 wherein: the filament is offset upwardly in a direction perpendicular to said reflector axis by an amount (.delta.) such that its light-emitting surface is substantially tangential to the axis (0x) and the surface of the central portion of the reflector is defined by the equation: ##EQU2## where: l=the filament half-length,
- f.sub.0 =the distance between the center of the filament and the co-ordinate origin; and
- Ox is the axis of the reflector, and the plane x0y is a substantially horizontal plane.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 85 08655 |
Jun 1985 |
FRX |
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BACKGROUND OF THE INVENTION
This is a continuation of co-pending application Ser. No. 755,070 filed on July 15, 1985, now abandoned.
The present invention relates to a motor vehicle dipped headlamp, in which the light beam is masked above two horizontal half planes set at different heights.
This type of masking, as described in U.S. Pat. No. 3,858,040, herein incorporated by reference and made a part hereof, is specifically adapted to the lighting standards in force in the USA, as defined, for example, by standard SAE J 579 C.
More precisely, the contour of the mask is defined by two horizontal half-planes, with the right-hand half-plane being on the same level horizontally as the axis of the headlamp and with the left-hand half-plane being displaced below the horizontal by about 1.5%.
Beams meeting these standards are generally designed using a headlamp having a bulb with a transverse filament which cooperates with a parabolic reflector of relatively long focal length so as to reduce the width of the beam and consequently minimize the extra thickness required for the deflecting prisms in the closure glass.
headlamps have also been proposed using an axial filament. In this case, the filament is focused in a parabolic reflector which is downwardly inclined in order to reduce the deflection required from the prisms in the glass, in other words, in order to reduce the maximum thickness of the glass.
The above-mentioned US Pat. No. 3,858,040 describes examples of both of these types of headlamps.
However, in both cases it is necessary to use a parabolic reflector having a relatively long focal length (about 29 mm to 32 mm) which therefore recovers relatively little flux.
A short focal length would give rise to excessively large images which would make it impossible to obtain the desired beam, unless high deflection prisms were used in the closure glass. The later is incompatible with the practicalities of molding (in particular when the closure glass is made of glass rather than plastic). In addition, high deflection prisms prevent a satisfactorily sharp cutoff due to the light dispersion which occurs because of the very marked relief of the glass.
Proposals have also been made to provide a reflector based on two half-paraboloids in order to reduce the unwanted side-effects due to the prisms in the glass. However, the reflector in such a headlamp has a surface discontinuity where the two half paraboloids meet. A reflector manufactured according to such teaching is difficult to make, and, in practice, the reflector will always be imprefect where the two half-paraboloids meet, thereby giving rise to light rays projected above the masking limit.
Preferred embodiments of the present invention provide dipped headlamps which remedy the above drawbacks and enable maximum recovery of the light flux emitted by the filament of the bulb.
The proposed dipped headlamp comprises, in conventional manner, a bulb, a reflector, and a closure glass in front of the reflector, together with means for masking the light beam above two horizontal half-planes at different horizontal levels.
According to the invention the headlamp has the following characteristics:
The bulb is an axial filament bulb without a masking cup.
The reflector comprises a deflecting surface without any discontinuity and suitable for forming images of the filament with all points of the image below a horizontal plane; and
Correction means are provided for angularly displacing said images upwardly to raise them to the level of the two horizontal masking half-planes.
In a first embodiment, the reflector is preferably inclined downwardly at an angle representative of the angular displacement of the left cutoff mask relative to the horizontal in a United States beam so as to begin left hand side masking. It is also inclined to the right by an angle corresponding to about half the angular extent of the concentration images from the sides of the reflector. The concentration images are raised to the horizontal level by the closure glass.
In another embodiment, the correction means comprise two lateral surfaces adjoining the reflector surface having the same equation as an extension thereof (taking account of the upward tilt) with the re-distributing closure glass then deflecting slightly in the vertical direction.
Preferably, in either case, the deflecting surface is suitable for forming images of the filament such that the highest point of each image is situated on a horizontal plane.
US Referenced Citations (5)
Continuations (1)
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Number |
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| Parent |
755070 |
Jul 1985 |
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Patent Grant
4797797
