Apparatus and method for controlling the light-range of motor vehicle headlights

The apparatus for control of a light-range of headlights of a motor vehicle includes two headlight orientation adjusting devices; at least one electro-optic sensor detecting actual values of light intensities of light reflected from an illuminated portion of the road; and an analyzer/control unit connected to the at least one electro-optic sensor and the adjusting devices to control the adjusting devices and the headlight orientation according to the sensor signal. To maintain the light-range of the headlights regardless of load conditions, the analyzer/control unit contains a memory device for storing data including set values of the light intensities for a desired headlight orientation and for storing other data including actual values of the reflected light intensities for actual headlight orientations when the headlights are set in the actual orientations; a comparator device for comparing the actual values for different actual orientations and the set values for the desired orientations; and a control device for controlling the adjusting devices according to the comparator device to set the headlights in various other actual orientations until the differences between the set values and actual values are minimized to determine the actual orientation closest to the desired orientation.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus and method for controlling 
the light-range of the headlights of a motor vehicle. 
A known apparatus for control of the light-range of the headlights of the 
motor vehicle includes an adjusting device connected with the headlights, 
at least one vehicle load condition sensor, and an analyzer/control unit 
connected to the adjusting device and the at least one load condition 
sensor. The load condition sensor or sensors detects the load condition of 
the motor vehicle and sends a sensor signal containing the information 
regarding the load condition to the analyzer/control unit which then sends 
a control signal to the adjusting device which adjusts the light-range. 
One apparatus of this kind is described in German Published Patent 
Application 23 33 983. This apparatus has an ultrasonic sensor, by which 
the distance between the chassis of the motor vehicle and the road is 
detected. Adjusting devices are connected with the headlights, by which 
their inclination or angular orientation is controlled. The sensor 
produces a sensor signal dependent on the distance of the chassis from the 
road and thus on the load condition of the motor vehicle. In the 
analyzer/control unit the sensor signal is processed and the adjusting 
device is controlled by it so that the light-range of the headlights is 
maintained constant with all the load conditions of the motor vehicle. In 
this known apparatus however it is presumed that the headlights have a 
correct base position when the vehicle is not loaded, from which they are 
adjusted or moved on loading of the motor vehicle. If the base position of 
the headlights is however incorrectly set when not loaded, an incorrect 
adjustment of the headlights results when the headlights are reset with 
the vehicle loaded. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an apparatus and method 
for control of the headlight range of the motor vehicle headlights. 
This objects and others which will be made more apparent hereinafter is 
attained in an apparatus for controlling a light-range of headlights of a 
motor vehicle on a road comprising at least one headlight orientation 
adjusting device connected with the headlights; at least one sensor 
detecting at least indirectly a load condition of the motor vehicle and 
producing a sensor signal depending on the load condition; and an 
analyzer/control unit connected to the at least one sensor and the at 
least one adjusting device, the analyzer/control unit receiving the sensor 
signal from the at least one sensor and controlling the at least one 
adjusting device and the headlight orientation according to the sensor 
signal to maintain the light-range of the headlights substantially 
constant. 
According to the invention at least one of the sensors is an electro-optic 
sensor which measures a state of light reflected from a portion of the 
road illuminated by the headlights in front of the motor vehicle and from 
obstacles located thereon; and the analyzer/control unit contains means 
for storing data including set values representing the state of the 
reflected light when the headlights are in a desired orientation, means 
for storing other data including actual values representing the state of 
the reflected light for an actual orientation of the headlights derived 
from the sensor signals from the at least one sensor when the headlights 
are set in the actual orientation; means for comparing the actual values 
and the set values and for forming differences between them; and means for 
controlling the at least one adjusting device to set the headlights in at 
least one other actual orientation repeatedly until the differences 
between the set values and actual values of the state of the light 
reflected are minimized to determine the actual orientation of the 
headlights closest to the desired orientation. 
The apparatus according to the invention for controlling the light-range of 
the headlights of the motor vehicle has the advantage that set values of 
the state of the reflected light from the illuminated portion of the road 
with the headlights in the desired orientation are stored in the 
analyzer/control device so that the accuracy of the headlight adjustment 
does not depend on the headlights being oriented in the correct position 
when the vehicle is not under load. 
The means for storing data can, of course, be a memory device, the means of 
comparing set values and actual values can be a comparator device and the 
analyzer/control device can be a microprocessor having a memory. 
In a preferred embodiment of the invention the electro-optical sensor has a 
plurality of individual light sensitive elements and each of the 
individual light sensitive elements senses light intensities from a part 
of the illuminated portion of the reflected light from the road in front 
of the motor vehicle. 
Advantageously in another preferred embodiment of the invention light 
intensities can be used as actual values representing the state of the 
light reflected and the means for comparing compares set values of the 
light intensities with actual values of the light intensities. 
In other embodiments of the invention the state of the light reflected is 
characterized by an illumination boundary of the light reflected and the 
means for comparing compares set values of the illumination boundary with 
actual values of the illumination boundary. 
In one embodiment the analyzer/control unit contains means for detecting 
changes in the state of the reflected light due to motion of the motor 
vehicle over the road and means for compensating for the changes due to 
motor vehicle motion over the road and in other embodiments it does not 
contain such means. 
In some situations only one electro-optic sensor is necessary. The 
electro-optic sensor can be attached to the motor vehicle or alternatively 
it can be connected with the headlight so as to move with it.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Two antidazzle headlights 10 are shown in FIG. 1 mounted on the front end 
of a motor vehicle chassis. Two adjusting devices 12, by which the 
orientation of the headlights 10 is adjusted, and two electro-optic 
sensors 14 are also mounted on the front end of the chassis. The 
antidazzle headlights 10 produce a light beam 16 which illuminates the 
road in front of the motor vehicle. The light beam 16 has a light-dark or 
illumination border or boundary 20 as prescribed for antidazzle headlights 
to avoid dazzling or partially blinding the drivers in the oncoming motor 
vehicle traffic. The antidazzle headlights can have a gas discharge lamp 
or a filament lamp as light sources. On loading of the motor vehicle the 
orientation of the chassis and the antidazzle headlights 10 attached to it 
changes. The position of the light-dark border or illumination boundary 20 
also varies so that a partial blinding of the drivers in the oncoming 
vehicular traffic could occur. To compensate for the change in inclination 
due to loading the orientation of the headlights 10 is adjusted by the 
adjusting devices 12. 
The adjusting devices 12 and the electro-optic sensors 14 are part of the 
apparatus for control of the light-range of the headlight 10. The 
apparatus has moreover an analyzer/control unit 22, which is connected 
with the sensors 14 and the adjusting devices 12. The sensors 14 can be 
attached to the chassis of the motor vehicle or to the headlight 10 and 
thus preform the adjustment of the headlights. Furthermore a electro-optic 
sensor 14 can be used for the adjusting devices of both headlights. 
The sensors 14 are pointed at the portion of the road and the obstacles on 
it illuminated by the motor vehicles in front of the motor vehicle. The 
sensors 14 respond to the reflected light from the illuminated portion of 
the road and the hindrances in the road and form electrical signals 
dependent on the state of the reflected light, which are fed to the 
analyzer/control unit 22. The sensors 14 can have focusing optics, by 
which the incident light is focussed on one or more light sensitive 
elements, for example photocells. Each portion of the focusing optics with 
the associated light sensitive elements is associated with a certain part 
of the region of the road 18 in front of the motor vehicle illuminated by 
the headlights. The analysis of the reflected light from the illuminated 
portion of the road and the obstacles present on it can occur according to 
a photometric or geometric method. 
In the photometric method actual values representing light intensities from 
individual parts of the illuminated region are produced by the 
electro-optic sensor or sensors. The actual values from various parts of 
the illuminated region are mapped by the several isointensity lines 24 
shown in the drawing, which are lines along which the actual values are 
equal. Sensor signals for each part of the illuminated region on the road 
are formed by the sensors and the sensor signals are fed to the 
analyzer/control unit 22. In the analyzer/control unit 22 set values of 
the state of the reflected light (or specifically the light intensities) 
are stored in the form of data, which should be independent of the loading 
of the motor vehicle. In the analyzer/control unit 22 the actual values 
representing the state of the reflected light (or specifically the light 
intensities from the sensors) are compared with the stored data 
representing the desired or set values and the differences between the 
actual values and set values of the illumination ratios are formed, 
according to which the adjusting devices 12 are controlled to eliminate 
the differences or deviation between actual or set values. 
Alternatively, the illuminated region of the road according to a geometric 
method the position of the illumination boundary, the light-dark border, 
on the road is detected. The position of the illumination boundary 20 can 
be determined by observing the strong decrease in light intensity values 
from parts of the illuminated region in the vicinity of the boundary. The 
sensors 14 form sensor signals as in the photometric method for each part 
of the illuminated region of the road 18, which are sent to the 
analyzer/control unit 22. In the analyzer/control unit 22 the desired or 
set values of the illumination boundary 20 when the headlights are in the 
desired orientation can be stored in the form of data, for example in 
memory locations if the analyzer control unit is a microprocessor. In the 
analyzer/control unit 22 the actual values for a number of actual 
orientations of the headlights are compared with the stored data 
representing the set values for the desired orientation and thus the 
deviation or differences between the set values and the actual values for 
the illumination border are determined. Depending on these differences the 
adjusting devices 12 of the headlights 10 are controlled by the 
analyzer/control unit 22 so that an actual orientation of the headlights 
is taken in which the deviation or differences are minimized. 
The above-described apparatus for control of the light-range can be 
operated in a first way or method only in a stationary motor vehicle. The 
apparatus can be activated by turning on the lights of the motor vehicle. 
The test of the set up and the adjustment of the headlights can occur as 
described below. The headlights 10 are moved stepwise by the adjusting 
devices 12 from one end position to another end position, i.e. between a 
maximum and minimum inclination of the headlights. This can be performed 
by a test program in the analyzer/control unit 22, by which the adjusting 
devices are correspondingly controlled. For each position of the 
headlights 10 the returning light from the road is registered by the 
sensors 14 and sensor signals from the sensor 14 are fed to the 
analyzer/control unit 22 and stored there. After performing the entire 
adjustment through all stepwise orientation values from maximum to minimum 
of the headlights 10 the actual values for each individual orientation or 
position are compared with set or desired values corresponding to the 
desired position or orientation of the headlights. Then the position or 
orientation of the headlights in which the deviation between actual and 
set illumination values is minimized is determined in the analyzer/control 
unit 22. Then adjusting devices 12 are controlled by the analyzer/control 
unit 22 so that the headlights are moved to the orientation corresponding 
to a minimum deviation between actual and desired or set illumination 
values. The adjusting devices are connected by a feedback connection with 
the analyzer/control unit to determine the momentary position of the 
headlights. 
Another possibility for a method of testing the set up and adjusting the 
headlights with the apparatus of the invention is an iterative method. The 
headlights 10 are moved from a first orientation into a second orientation 
by the adjusting devices 12, which are controlled by the analyzer/control 
unit 22. In both orientations the actual illumination values of the light 
returned from the road are measured and are fed to the analyzer/control 
unit 22. In the analyzer/control unit the deviation of the actual 
illumination values from the set or desired values is measured and it is 
determined whether the deviation of the first or the second orientation is 
the greater or the lesser. If the deviation decreases from first to second 
orientation or position, the headlights are moved further in the same 
direction as the direction from the first to second orientation or 
position until the deviation begins to increase again so that then the 
last orientation of the headlights before the increase corresponds to the 
desired position in which the deviation is minimum. However if the 
deviation increase from first to second position, the headlights are moved 
in the opposite direction until they reach the optimal position in an 
iterative manner. 
It is possible with both the above methods to perform adjustment of the 
orientation of the headlights first with the headlights on the side of the 
vehicle facing opposing traffic and then with the headlights on the 
opposite side of the vehicle. The order of the side chosen can of course 
be reversed. 
In another embodiment of the invention the apparatus for control of the 
light-range of the headlights can be installed so that also it can operate 
with the vehicle moving, i.e. it can perform a dynamic adjustment of the 
headlights. The set up and the control of the headlights is advantageously 
performed with an iterative method as described above in this embodiment. 
The effect of the condition of the road and the course of the road as the 
vehicle travels over it must not be considered in adjusting the 
headlights, so that for example a suppression of these influences on the 
illumination reaching the sensors must be performed by a suitable 
electronic circuit in the analyzer/control unit. The electro-optical 
sensors 14 can also be used for other purposes, for example detection of 
the edges of the street. Also whether to switch from high beams to low 
beams or dim light can be determined with the help of the sensors and this 
switching can be automatically effected by the analyzer/control unit 22. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in an 
apparatus and method for control of the light-range of motor vehicle 
headlights, it is not intended to be limited to the details shown, since 
various modifications and structural changes may be made without departing 
in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.