Method and system for providing an optical signal at the rear of a vehicle to warn the driver of a following vehicle

The present invention relates to a method and a system for providing an optical signal at the rear of a vehicle to warn the following traffic of an ongoing electronic control intervention in the vehicle behavior. Such an electronic control function can be for instance ABS, TCS or automatic yaw control. A preferred embodiment of the invention utilizes the center brake light of a vehicle to emit an intermittent optical signal during electronic control. In case of ABS, the two side brake lights shine continuously to indicate a brake pedal actuation while the center brake light flashes in an on/off- mode according to the electronic antilock control.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for providing an optical signal 
appearing at the rear of a vehicle to warn the driver of a following 
vehicle. 
Such an optical signal is, for instance, a brake light indicating a brake 
pedal actuation. Brake lights are prescribed for all automotive vehicles. 
In some countries, for four-wheeled vehicles even a third, central, brake 
light is required. The purpose is to provide the following traffic with 
the information of an imminent or ongoing deceleration. 
Nowadays, a majority of vehicles is equipped with an electronic control 
system comprising at least one of the following functions: antilock brake 
system (ABS), traction control system (TCS), automatic yaw control (AYC). 
All these functions influence the behavior of the vehicle without a 
respective driver's action. While ABS reduces the brake force of 
individual wheels during a pedal actuated braking operation when the 
applied brake force threatens to lock a wheel, the other electronic 
control systems are capable of applying a brake force to selected or all 
wheels under certain conditions according to preestablished control 
algorithms. Thus, an deceleration of the vehicle can occur, either due to 
an improved brake efficiency during a pedal-actuated brake operation 
supported by ABS or due to a so-called "active" brake operation through 
TCS or AYC operation provoked by excessive traction slip or unstable 
vehicle behavior during cornering. In each case, such vehicle deceleration 
may not be expected by the driver of a vehicle behind the decelerating 
vehicle. 
To provide a warning for the driver of a following vehicle, German patent 
No. 43 05 186 proposes an additional warning light at the rear of a 
vehicle to be switched on dependent on a hazard value. The hazard value is 
derived by time integration of the current vehicle deceleration over a 
certain time period. If the hazard value exceeds a certain threshold, the 
warning light is activated and remains shining until the hazard value has 
decreased again. During ABS control, the deceleration is multiplied by an 
amplification factor so that the threshold is reached earlier than without 
ABS intervention. 
According to German patent No. 43 05 186, for deriving the hazard value, 
the vehicle is equipped with an additional accelerometer for measuring the 
vehicle deceleration, which causes additional costs. 
While a deceleration-dependent warning is an asset compared to only 
pedal-actuated brake lights, it is disadvantageous that, on the one hand, 
the warning light will always shine up even when a deceleration occurs 
entirely due to driving uphill or to braking forces that are normal for 
the circumstances and can be easily foreseen by following drivers. In such 
cases, no additional warning is needed. On the other hand, no warning will 
be given by known systems in situations that require an intervention of an 
AYC or TCS. For instance, if a vehicle is equipped with an AYC, an 
inadequate cornering maneuver can be compensated by selective brake 
application of the inner rear wheel in case of understeering and of the 
outer front wheel in case of oversteering. By the driver of a following 
vehicle driving in the same manner, but without such an automatic control 
function, the cornering maneuver is approached without advance notice of a 
dangerous condition, and the driver has no reason to reduce speed since 
the vehicle ahead manages the situation without a sign of instability. For 
the following vehicle, however, the same behavior can be fatal. Similar 
considerations apply for low-friction road surfaces when only an 
intervention of TCS can maintain a sufficient traction. 
OBJECT OF THE INVENTION 
An object of the present invention is to provide a method for an improved 
optical warning at the rear of a vehicle in situations that can be 
hazardous for the following traffic. 
Another object of the invention is to provide such a warning method which 
does not cause an overflow of warnings resulting in a reduced attention or 
even unnecessary distraction of following drivers. 
Still another object of the invention is to provide a low-cost system 
performing the method above. 
SUMMARY OF THE INVENTION 
These objects are achieved by an optical signal at the rear of the vehicle 
appearing during intervention of an electronic controller influencing the 
vehicle behavior. The driver of a following vehicle is always warned when 
a situation occurs which has activated electronic support. If the 
following vehicle is not equipped with an electronic controller, the 
warning appears sufficiently early to provoke an appropriate driver's 
reaction which can prevent serious accidents. 
The influence that activates the optical signal can be electronic brake 
control as well as electronic reduction of the driving torque, for 
instance throttling a combustion engine, for this measure also causes a 
vehicle deceleration. 
It is not to be feared that the optical warning according to the invention 
might result in an overflow of information with the effect that such a 
warning is ignored, for an electronic control of the vehicle behavior is 
always an exceptional intervention occurring only in very rare cases and 
deserves the attention of the following driver. 
An even higher degree of safety is achieved if the signal generated during 
electronic control differs from the standard brake light. This increases 
the information level of the following traffic since an inappropriate way 
of driving can be distinguished from a normal brake pedal actuation. 
Such a signal can be provided by a separate light completely independent 
from the brake light or by one or more brake lights shining in a different 
mode such as flashing during electronic control. The latter is a very 
inexpensive way to increase the information level of the following traffic 
because no additional lights are necessary. This allows the invention to 
be installed as an add-on system for new and used vehicles.

DETAILED DESCRIPTION OF THE DRAWINGS 
In FIG. 1, a vehicle 1 is equipped with brake lights 2, 3 and 4 for 
indicating an actuation of a brake pedal 5, here shown outside the vehicle 
in order to simplify the drawing. The third light 4 (preferably a brake 
light) is located in a central, higher position compared to the two other 
brake lights 2 and 3 located one on each side. An electronic control unit 
6, capable of influencing the vehicle behavior by means of ABS, TCS and 
AYC, has no impact on the two brake lights 2 and 3, but only on the center 
brake light 4, although it would be feasible to have all three brake 
lights 2, 3 and 4 influenced by the controller. The solid arrows pointing 
from the brake pedal 5 to the brake lights 2, 3 and 4 imply a constant 
signal while the brake pedal 5 is depressed. The dashed line of the arrow 
pointing from the electronic control unit 6 to the center brake light 4 
implies an intermittent signal appearing whenever an electronic control of 
the vehicle behavior is carried out. The electronic control may influence 
either or both of braking forces and driving torque of the drive unit. 
A simplified plotting of the system is shown in FIG. 2. The brake pedal 5 
acts on a first relay 7 connecting the brake lights 2 and 3 to a power 
source 8. This relay 7 is of a comparably simple structure such as a brake 
light switch of known implementations. It works in the known way, 
switching the brake lights 2 and 3 on while the brake pedal 5 is 
depressed. 
The center brake light 4 is connected to the power source 8 via a second 
relay 9. This second relay 9 is controlled by the brake pedal 5 as well as 
by the electronic controller 6. Within this relay 9, the electronic 
controller 6 has priority over the brake pedal 5. Thus, the center brake 
light 4 will show the standard brake signal during normal pedal-actuated 
braking as long as no electronic intervention is necessary. As soon as the 
electronic controller 6 influences the vehicle behavior, the center brake 
light 4 will generate an intermittent signal while the two other brake 
lights 2 and 3 continue their standard signal. Should the ABS control 
finish during brake pedal actuation, the center brake light 4 returns to 
the standard brake signal. If the ABS control continues until the brake 
pedal 5 is released, the signal indicating an electronic control will go 
out at the same time as the two side brake lights 2 an d 3. 
If an electronic control takes place without a simultaneous actuation of 
the brake pedal 5, only the center brake light 4 will send an intermittent 
signal while the two side brake lights 2 and 3 are not activated. 
Suitable frequencies for the intermittent signal are in a range of 1 to 10 
Hz. 
Though only one certain embodiment has been described, the invention is not 
limited to the features set forth above. More than one or even all brake 
lights can send the signal for electronic control. This signal can as well 
appear as alternating flashes changing between the center brake light 4 
and the two side brake lights 2 and 3 which may shine at the same time or 
one after the other. The signal itself can comprise a change of the light 
color, intensity or shape. A change of the signal shape does not only 
include a flashing on/off-mode, but also, for instance, a hi/low-mode or a 
hi/low/off-mode. The signal for electronic control can be superimposed on 
the continuous standard brake signal.