Brief Description Of Components
The following components and control units provide signals for the adaptive headlight system:
- CAS: Car Access System
The Car Access System supplies signals for the terminal management (e.g. terminal 15 ON).
The adaptive headlights control unit is activated when terminal 15 is switched ON.
- Light switch
The rotary switch for the side lights and dipped headlights differs depending on the vehicle equipment level (adaptive headlights, automatic driving lights control, automatic or manual headlight-range adjustment). For the adaptive headlights function to operate, the light switch must be set to position "A" ("A" = "automatic driving lights control" and "adaptive headlights").
- Turn-signal/main-beam switch
The main-beam headlights are switched on and off with the turn-signal/main-beam switch (by pressing or pulling the switch). The adaptive headlights function operates with both dipped and main-beam headlights.
- SZL: Steering Column Switch
The SZL control unit forwards the signals from the turn-signal/main-beam switch to the adaptive headlights control unit.
- E60, E61, E63, E64, E65 and E66
- E70, E81, E87, E90, E91, E92, E93
The steering column switch cluster forwards the signals from the turn-signal/main-beam switch to the footwell module (FRM).
- Ride-height sensors
If the special equipment "Adaptive headlights" is fitted, the adaptive headlights control unit evaluates the signals from the ride-height sensors. This is because: the adaptive headlights control unit also controls the automatic headlight-range adjustment.
The automatic headlight-range adjustment feature adjusts the vertical aim of the headlights to compensate for variations in the vehicle tilt angle (e.g. when the vehicle is laden, and under braking and acceleration in dynamic driving situations).
- Brake light switch
If the special equipment "Adaptive headlights" is fitted, the signals from the brake light switch are read by the adaptive headlights control unit.
In addition, the brake light switch signal is also a signal for automatic headlight-range adjustment, see Ride - height sensors.
- Position sensor
- E60, E61
- E65, E66
Hella headlights have a position sensor.
The position sensor in the positioner module for the bi-xenon headlights supplies a signal for the horizontal movement of the headlights.
- Zero-position sensor
- E63, E64
- E70, E81, E87, E90, E91, E92, E93
Automotive Lighting headlights, previously Bosch, have a zero-position sensor.
The zero-position sensor registers the horizontal movement of the headlight.
- EGS control unit or reversing light switch
When reverse gear is engaged, the headlights are moved to the straight-ahead position.
- On vehicles with automatic transmission, the EGS control unit provides the "Reverse gear engaged" signal. (EGS: electronic transmission control).
- On vehicles with manual transmission, the signal is supplied by the reversing light switch.
- Rain-light sensor for automatic driving lights control
The rain-light sensor measures the ambient brightness outside the vehicle.
- In twilight conditions, the rain-light sensor transmits the message "Twilight" so that the automatic headlight- range adjustment can activate dipped headlights. The headlights are tilted up and down as required, but they are not yet moved towards the bend in the road.
- In darkness, the rain-light sensor sends the message "Darkness". The adaptive headlights are then activated when the vehicle is cornering. The headlights are moved to the left or right:
- Steering-angle sensor and DSC sensor
The steering angle sensor and DSC sensor (DSC = Dynamic Stability Control) supply signals for the adaptive headlights to the adaptive headlights control unit. These signals are evaluated as follows, depending on the vehicle's speed:
- Vehicle speeds up to 30 km/h:
The adaptive headlights function is controlled using the information from the steering angle sensor (in the steering column switch cluster).
- Vehicle speeds between 30 km/h and 50 km/h:
In the 30 to 50 km/h speed range, there is a continuous transition in signal evaluation: from the evaluation of signals sent by the steering angle sensor to evaluation of the signals sent by the yaw-rate sensor (in the DSC sensor).
- In extreme dynamic driving situations,
e.g. if the vehicle starts to skid or fishtail, even at speeds less than 50 km/h, the signals from the yaw-rate-sensor are considered.
If the vehicle starts to skid or fishtail, the headlights will move to the straight-ahead position. The headlights are not moved until the vehicle has stabilized.
- Vehicle speeds over 50 km/h:
At speeds upwards of 50 km/h, the signals from the yaw-rate sensor (in the DSC sensor) form the primary basis for control of the adaptive headlights function.
Reason: For a constant cornering radius, the steering angle required increases disproportionately with speed. In addition, the steering angle required also depends on the coefficient of friction of the road surface.
Yaw rate is directly proportional to speed. For this reason, the yaw rate is always the most suitable measure for controlling the adaptive headlights at high speeds.
Even at high speeds, however, the steering angle sensor signal is used to detect (predict) the driver's commands in advance . This prediction is important: The yaw rate signal is not supplied until the vehicle has responded to the steering wheel movement.
The steering-angle sensor signal is disabled so that rapid, momentary steering adjustments do not affect the adaptive headlights function.
A number of control units are involved in the adaptive headlights system (see CAS, EGS, SZL). Depending on the model series and model version concerned, the adaptive headlights are actuated by the following control units:
- Vehicle speeds up to 30 km/h:
- AHL: Adaptive headlights
- E60, E61, E63, E64, E65, E66 up to 03/2005
The AHL control unit actuates the adaptive headlights.
For safety reasons, the AHL control unit is also responsible for the automatic headlight-range adjustment. This is because: Oncoming traffic must not be dazzled by the adaptive headlights. If a headlight sticks in an unfavorable position, the AHL control unit will attempt to move this headlight down (using the stepper motors in the automatic headlight-range adjustment).
The AHL control unit is connected to the PT-CAN.
- LM: Light module
- E60, E61, E63, E64, E65, E66 from 03/2005
From 03/2005, the AHL control unit is integrated in the light module.
The light module (LM) controls and monitors all vehicle lights. Information is transmitted and received via the KCAN data bus.
The light module actuates the indicator light for the adaptive headlights (on the light switch).
- FRM: Footwell module
- E70, E81, E87, E90, E91, E92, E93
The footwell module controls the exterior lighting and the adaptive headlights.
The footwell module thus takes the place of the light module and the AHL control unit.
The footwell module actuates the indicator light for the adaptive headlights (on the light switch).
The footwell module has its own system description.
The following additional control units are involved in the adaptive headlights:
- SMC: Stepper motor controllers
The stepper motor controllers control the stepper motors in the headlights (for the automatic headlight-range adjustment and for the adaptive headlights). The stepper motor controllers are not capable of self-diagnosis. The stepper motor controllers are diagnosed and encoded via the control unit for adaptive headlights.
- SGM: Safety and gateway module
- E60, E61, E63, E64 until 09/2005 and E65, E66
The safety and gateway module (SGM) is the interface between the two data buses K-CAN and PT-CAN. Thus, all information exchanged between the light module and the AHL control unit passes through the SGM. Information from the yaw-rate sensor (in the DSC sensor) is also fed through the SGM to the AHL control unit.
- KGM: Body gateway module
- E60, E61, E63, E64 from 09/2005
The vehicle electrical system was changed from 09/2005.
As a result of the change, several control units were discontinued and some control unit functions were integrated into new control units.
The new body gateway module (KGM) supersedes the safety and gateway module (SGM) previously fitted, the door modules and the micro-power module.
- Xenon-headlight control unit
The xenon-headlight control unit actuates the bulb in the bi-xenon headlights.
The xenon-headlight control unit is not capable of self-diagnosis. The xenon control unit is monitored by the light module (E70, E81, E87, E90, E91, E92, E93: footwell module).
The following components are controlled:
- Headlights
Option 524 "Adaptive headlights" is only available in conjunction with option 522 "Xenon dipped and main-beam headlights". This means that bi-xenon headlights are employed.
- Stepper motors for the adaptive headlights
The stepper motors turn the positioner modules in the bi-xenon headlights.
The stepper motors move the headlights vertically and horizontally (vertically = up and down for automatic headlight range adjustment;
horizontally = left and right for the adaptive headlights function).
The positioner modules execute the movement.
- Indicator light on the light switch
The indicator light (green LED) next to the "A" (= "automatic driving lights control" and "adaptive headlights") has 2 display functions:
- The indicator light lights up permanently when the automatic driving lights control or adaptive headlights function is switched on (= light switch in position "A").
- The indicator light flashes
if a fault develops in the adaptive headlight system.
- E60, E61, E63, E64, E65 and E66:
The indicator light is actuated by the light module.
- E70, E81, E87, E90, E91, E92, E93:
The indicator light is actuated by the footwell module.
From 09/2007, the fault indicator in the form of the indicator lamp on the light switch flashing is discontinued due to legal stipulations.
From 09/2007 system fault will be indicated by a Check-Control message in the instrument cluster.