SAE TECHNICAL
`PAPER SERIES
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`980010
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`Adaptive Headlamp: A contribution for Design
`and Development of Motorway Light
`
`Giorgio Manassero and Maria Teresa Dalmasso
`Magneti Marelli - Lighting Division
`
`Reprinted From: Automotive Lighting Technology
`(SP-1323)
`
`International Congress and Exposition
`Detroit, Michigan
`February 23-26, 1998
`
`400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A.
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`Tel: (724) 776-4841 Fax: (724) 776-5760
`
`VWGoA EX1019
`U.S. Patent No. 9,955,551
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`ISSN 0148-7191
`Copyright 1998 Society of Automotive Engineers, Inc.
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`980010
`Adaptive Headlamp: A contribution for Design and
`Development of Motorway Light
`
`Giorgio Manassero and Maria Teresa Dalmasso
`Magneti Marelli - Lighting Division
`
`Copyright © 1998 Society of Automotive Engineers, Inc.
`
`ABSTRACT
`
`A major breakthrough in improving visibility, safety and
`comfort under all driving conditions is given by a head-
`lamp with adjustable light intensity and beam pattern
`according to the vehicle speed, steering wheel angles
`and different driving conditions.
`The configuration of this adaptive or intelligent headlamp
`will be achieved in two phases, by implementation of sim-
`ple functions, i.e. motorway beam pattern, followed by a
`combination of them in a second phase. For the new
`adaptive headlamp one should make use of powerful
`light sources like the Gas Discharge Bulb and of sensors
`for road surface status, speed and steering wheel angle.
`The optical design of the adaptive headlamp is more
`complex than for conventional headlamps and must take
`into account new requirements like the continuous transi-
`tion between the low and high beam positions.
`In this paper we describe the design and prototyping
`phases for an adaptive headlamp whose beam pattern
`and aiming condition can be varied by the use of actua-
`tors. The results of the optical simulations are given and
`compared with the corresponding prototype measure-
`ments.
`
`INTRODUCTION
`
`The problem of visibility during night driving conditions is
`not always considered as an important constraint during
`the design and development of new vehicles. Very often
`car-makers reduce the space allocated to the lighting
`components and define them for design requirements
`only. Therefore for component suppliers it is difficult to
`achieve high photometric performances. Under these
`strict conditions, car suppliers can achieve good perfor-
`mances by means of new lighting techniques (e.g.
`numerically calculated reflectors) and light sources (e.g.
`HID bulbs and systems): the new products guarantee a
`good light flux, as requested by international regulations,
`but the beam pattern and aiming are fixed. Therefore
`they do not always provide the best visibility under differ-
`ent driving and weather conditions.
`
`1
`
`For an overall improvement, it is necessary to dynami-
`cally modify the beam pattern and light intensity during
`driving, and to account for road and weather conditions
`by means of a wide variety of sensors. A first step in the
`aforementioned direction is to develop a headlamp which
`is able to improve visibility during one of the following
`conditions: rain and fog, on curves, on motorways and in
`town [1]. The following step will be to implement more
`than one function, to suit more than one driving condition,
`and offer a good comfort during transition between driv-
`ing situations, i. e. transition between low speed and high
`speed.
`This paper will describe the development of a Motorway
`headlamp able to vary its photometric characteristics with
`speed. The headlamp will try to reduce the aiming angle
`and the width of the beam as the vehicles speed
`increases. These operations will be automatic with the
`aid of sensors, actuators and electronic boards. The pur-
`pose, as for all adaptive functions, is to always provide an
`optimal beam. This will increase driving safety and com-
`fort. The best visibility characteristics should be obtained
`without causing dazzling of the oncoming vehicles. Sev-
`eral numerical simulations, laboratory and road tests are
`being performed to identify the best strategy to achieve
`the proposed goals.
`
`FUNCTION DESIGN
`
`While driving on a Motorway the high speed and low road
`lighting require better visibility. In particular when driving
`at high speed, foreground illuminance is less important,
`while a high light depth is very useful to detect vehicles
`running ahead.
`Beam modifications must be implemented without daz-
`zling oncoming vehicles: this paper examines the possi-
`bility of varying the low beam distribution without
`trespassing the horizontal line.
`It is possible to obtain an increase of illuminance in two
`ways. The first is to decrease the aiming angle of the light
`beam and the second is to change the beam shape, to
`reduce the beam divergence.
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`Research and experimental activity were divided into two
`parts:
`1. The study and set-up of a system capable of chang-
`ing the aiming of the beam depending on the car
`speed.
`2. Computer simulations and analysis of optical solu-
`tions capable of changing beam shape with the car
`speed.
`
`VARIABLE AIMING
`
`In varying the beam aiming angle, the attention was
`focused in the mechanical movement of the reflecting
`surface. The angle was varied from -1% to 0%.
`To test this solution, a prototype was set up, where the
`reflector movements were implemented by means of
`stepper motors. The relationship between speed/move-
`ments is a linear one: the starting speed was fixed, and
`several slope parameters were adopted to identify the
`optimal value.
`The system was assembled onto a vehicle and some
`road testing was carried out. The following variables were
`chosen in order to carry out a preliminary Design Of the
`Experiment.
`• starting speed
`• slope of the movement
`• dynamic leveling.
`The set parameters are adjustable by acting on the elec-
`tronic control unit, which was positioned in the vehicle. At
`this stage, the optical part analysis was ignored and an
`elliptic headlight with a gas discharge lamp was chosen.
`The goal is to establish which starting speed and slope
`would increase the driver’s comfort. The influence of
`dynamic leveling on the variation of aiming due to speed
`increase was also investigated. In some configurations it
`may happen that dynamic leveling cancels the effect of
`the applied correction for the speed increase.
`Tests were carried out on a two lane track. The partici-
`pants were divided into drivers, static observers, and
`dynamic observers (driving a crossing car). All partici-
`pants were asked to evaluate three different parameters:
`illuminance, glare and comfort.
`According to our test results the best configuration has a
`starting speed of 90 km/h and a slow variation of aiming,
`slope = 0.125 (% / 10 km), in order to achieve the 0 %
`aiming when speed is increased up to 170 km/h: Fig. 1
`shows the slope diagram, with four different speeds. The
`dotted one is the slope that the participants have consid-
`ered the best, from the point of view of comfort and visi-
`bility.
`
`2
`
`Figure 1. Slope diagram for a starting speed of 90 km/h.
`
`The interaction of this system with dynamic leveling was
`considered useful in increasing driver's comfort.
`
`VARIABLE BEAM SHAPE
`
`According to the tests carried out on the system
`described above, the change of aiming is neither optimal
`nor sufficient yet if we want to obtain a real increase of
`the driver's comfort.
`Further actions are necessary to improve illuminance dis-
`tribution and the cut off line: a variable beam shape could
`enhance visibility, together with a variable aiming.
`The goal is to obtain a gradual change of the beam
`shape, starting for example from a low beam configura-
`tion. As an example, it is useful to decrease the horizon-
`tal divergence and increase illuminance in HV, while the
`car speed increases. This is because it is demonstrated
`that at high speed foreground light is irrelevant for safety,
`while concentrate light in the central part of the screen
`increases visibility.
`As a constrain on this procedure the redirected light
`shouldn't go above the horizontal line not to dazzle
`oncoming vehicles.
`A preliminary analysis of different procedures was per-
`formed taking into account, for instance, the possibility of
`changing the beam shape with the movements of parts in
`the reflector structure.[ 2] [3]
`Fig. 2 and 3 represent two different reflectors a parabolic
`and a segmented one that we simulated with an optical
`design and analysis software.
`
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`Simulations were performed in both cases with a gas dis-
`charge bulb D2S because of its high efficiency and low
`heating. Fig. 4 shows the D2S apodization diagram.
`
`Figure 2. Parabolic reflector.
`
`The low beam configuration for the parabolic reflector
`was obtained with a shaped mask, fixed to the reflector,
`that cuts rays from the lower part of the parabolic and
`models the 15 degree cut-off line. The idea was to repro-
`duce the H4 configuration with a monofilament lamp.
`
`Figure 4. Apodization diagram of the Gas Discharge
`Lamp D2S (x axis is the optical axis)
`
`A large diameter was chosen for the parabolic reflector to
`increase the luminous intensity.
`Dimensions of parabolic reflector (focus=26 mm):
`diameter: 165 mm
`Dimensions of segmented reflector:
`front section: 150 x 80 mm.
`In the case of the parabolic segmented reflector, sector 1
`and 2 were tilted around the y axis, with a rotation angle
`of 1.5 degrees. P1 and P2 are the points about which
`reflector sectors were rotated as shown in Fig. 5.
`
`Figure 3. Segmented reflector
`
`Figure 5. Ray-tracing and isolux diagram of the
`segmented reflector.
`
`In the case of the parabolic reflector, the reflector lateral
`segments were rotated around the y axis about points T1
`and T2, with a rotation angle of 1.5 degrees, as shown in
`Fig. 6.
`
`3
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`Figure 6. Ray-tracing and isolux diagram of the
`parabolic reflector.
`
`The isolux diagrams show an increase of the Emax
`value and, as a consequence, an useful increase of illu-
`minance in HV.
`The second solution that we studied in details regarded
`the effects of source displacement on the beam light dis-
`tribution, for different reflectors geometries.
`Simulations were performed on the displacements of the
`source near the focus, along the optical axis, for the
`above systems. Further simulations were performed on
`an elliptical system (elliptical reflector, obscurator mask
`and a condenser)
`In all cases the source used was the Gas Discharge
`Bulb, D2S, because hot filaments do break during the
`movement of the lamp, and because of the high effi-
`ciency of the discharge bulb.
`Dimensions of elliptic reflector (focus=40 mm):
`diameter: 85 mm
`A preliminary investigation on the different reflectors effi-
`ciency while moving the source along the optical axis
`was carried out. Our optical design and analysis software
`evaluated the percentage of the emitted flux collected on
`an infinite screen positioned 25 m ahead of each optical
`system.
`Fig. 7 shows the graphs of these optical simulations for
`each different system considered. The shift values (mm)
`of the light source around the focus are on the abscissa,
`the percentage values of flux collected by the screen are
`on ordinate axis.
`
`Figure 7. Flux percentage vs. source shift.
`
`When the source is moved from the vertex of the reflector
`to the outer region (from negative to positive values of
`shifts), the luminous flux decreases for the parabolic
`reflector. For both the elliptic reflector and the segmented
`reflector there is an increase of flux only in a region very
`close to the focal point.
`All the evaluations were done considering only rays col-
`lected by a fixed angular portion of the detector screen.
`Fig. 8 shows the qualitative changing of the Emax value
`when moving the source around the focal point (P) of the
`segmented reflector, around the focus (F) of a parabolic
`surface and around the focus (F1) of an elliptical reflector.
`Three different parabolic reflectors were considered, with
`the same outer dimensions but with different focus val-
`ues: 21, 26 and 30 mm.
`
`4
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`One can clearly see that maximum illuminance values
`occur when the source is
`i) centered in the focal point in the case of parabolic
`reflectors,
`ii) for positive shift in the case of elliptical reflector
`iii) for negative shifts in the case of segmented reflec-
`tors.
`
`Figure 8. Qualitative evaluation of Emax vs. source shift.
`
`Additional simulations were done on the light distribution
`and the isolux curves for the segmented, parabolic and
`elliptic reflector, with different source positions in each
`case, in order to verify the change of beam shape.
`At first the emitting region of the source was centered in
`the focal point. It was then shifted along the optical axis
`
`around the focus F of the parabolic reflector or the point
`P of the segmented reflector or the focus F1 of the ellipti-
`cal reflector.
`Total shift was 3.5 mm in the parabolic case, 2.6 mm for
`the segmented reflector and 3.5 mm for the elliptic reflec-
`tor. The different shift was established on the different
`geometry characteristics of the optical systems shown.
`Simulations were carried out taking into account only
`reflected light and neglecting rays coming directly from
`the source, a reflectance of 80% was considered. In all
`the cases a vertical shift was necessary to project light
`below the horizontal line.
`Diagrams shown in Fig. 9 demonstrate that the seg-
`mented reflector considered gives a divergence of 4
`degrees with a total shift of the source of 2.6 mm, but a
`lot of light is projected in the lower region. Parabolic
`reflector gives a 7 degrees divergence with a total shift of
`3.5 mm and the light is concentrated on a small area,
`with unchanged beam shape. The elliptical system
`doesn’t give an useful divergence variation for our pur-
`poses.
`Further evaluations will be necessary in order to evaluate
`not only the variation of the divergence but also the illumi-
`nance values, considering appropriate outer lenses for
`the parabolic and segmented reflectors.
`
`5
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`Figure 9. Light pattern for the three different optical systems considered, with some source position shifts around the focal
`points
`
`CONCLUSION
`
`REFERENCES
`
`Some results on the Motorway Light have been pre-
`sented with HID bulb and systems mounted on a test car.
`This shows that the movement of the aiming during
`speed change increases visibility and driving comfort. An
`improvement of photometric characteristics and optimiza-
`tion of the beam pattern is also required. To reach this
`goal some simulations were carried out using different
`optical systems. These simulations are essential to
`define the most suitable solution for the future.
`
`1. AFS - Advanced Frontlighting Systems, EUREKA Project
`N. 1403
`2. R. Neumann - Improved Low Beam by use of segmented
`headlamp systems. SAE Technical Paper Series 870063,
`1987
`3. H. Hogrefe, R.Neumann - Adaptive Light Pattern - A new
`way to improve light quality. SAE Technical paper series
`970644, 1997
`
`6
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