Automatic Headlight Beam Adjustment
94 - Automatic Headlight Beam Adjustment
NOTE: The system is adapted to the different types of vehicles by programming the vehicle specific parameter with the aid of the PIWIS tester.
The automatic headlight beam adjustment function is integrated into the front end control unit. Dynamic automatic headlight beam adjustment automatically corrects the level of the headlight beam such that neither the vehicle's load nor the pitching movements resulting from the vehicle's driving dynamics can dazzle oncoming traffic when dipped beam is switched on, while at the same time ensuring an adequate range of vision for the driver.
This results in increased driving safety while at the same time reducing the strain on the driver.
Functions
NOTE:
- Recalibration is always to be carried out and the headlight setting is always to be checked when dismantling the axle sensors or a component connected to the sensors.
- The same also applies, of course, when replacing the front end control unit. Coding of the module concerned is to be carried out beforehand in this case.
The sensors on the front and rear axles (3, 4) supply signals to the controller (2) which are proportional to the spring deflection of the body at these points. This results in a non-linear characteristic for the front and rear axles sensors. On the basis of this characteristic, a micro-processor controller calculates the vehicle's pitch angle and the required position of the actuators (1) in the headlight for the purposes of headlight beam adjustment.
A signal proportional to the vehicle speed (wheel speed) is supplied directly via a signal line from the ABS / PSM control unit. The system distinguishes between cruising and accelerated driving by evaluating the wheel speed signal. During driving, interfering signals which are super-imposed over the sensor signal as a result of the road surface (bumps and pot holes) are filtered out. The system detects poor road surfaces and responds accordingly by reducing actuation of the stepping motors or shutting them down completely.
The system responds very quickly to braking or acceleration. The response time lies in the range of 0.1 seconds, i.e. the motor begins to adjust the headlights no later than 0.1 seconds after commencement of the pitching movement. This eliminates the risk of dazzling oncoming traffic and ensures the maximum depth of illumination for the driver.
When the vehicle is stationary, the vehicle's inclination is calculated from the sensor signals and the headlight settings are corrected according to the difference between their required and actual positions. The full scope of functions is maintained when high beam is switched on.
The system functions on the basis of the following input values from the vehicle:
- Ignition, terminal 15 (power supply for the control unit)
- Wheel speed signal, supplied via CAN data line or signal line
- Dipped beam, terminal 56b (or parking light, terminal 58)
- High beam, terminal 56a, data supplied via CAN data line
- Ambient brightness, supplied as CAN signal from the air conditioning control unit/sun sensor
Ignition "ON"
When switching on the ignition, referencing of the stepping motors is carried out, i.e. the motor moves the reflector in the direction of "maximum dip" up to the stop incorporated in the motor. The calculated position is then reached. Renewed referencing is carried out only after terminal S has been inactive. The referencing frequency is tested during the trial phase and the pertinent conditions are finalized.
Dipped beam "ON"
NOTE: In day mode, the headlights are operated with increased damping whatever the road conditions. When switched off the headlights are moved into the position in which they were located the last time the vehicle load alignment was carried out. In case of CAN failure or implausible signals from the a/c control unit, automatic headlight beam adjustment is only activated "dipped beam ON" applies.
When dipped beam (or daytime driving lights) are switched on and an appropriate degree of darkness applies, the control unit switches to normal operational status, i.e. the stepping motors are operated in accordance with the spring deflection values detected by the sensors and the subsequently determined vehicle inclination values. Suitable filters are employed according to the characteristics of the road surface and the vehicle speed, providing the driver with sufficiently smooth response.
High beam "ON"
Automatic headlight beam adjustment remains active when high beam is switched on.