Lane Departure System: Description and Operation
Lane Change Warning
Lane change warning (SWW)
The lane change warning (SWW) is a new driver assistance system. The lane change warning supports the driver when changing lanes. To do so, the lane change warning uses 2 radar sensors to monitor the traffic behind and to the side of the vehicle.
The lane change warning provides the following advantages:
- The lane change warning can detect traffic situations in which a lane change could lead to danger. The driver is then notified and warned in 2 stages (warning lamp in the exterior mirror, vibration on the steering wheel).
- Traffic situations of this nature occur, for example, when vehicles approach at high speed from the rear. During darkness in particular, the driver is unable to asses these situations accurately. The radar sensors work absolutely independently of the lighting conditions.
- Another possible danger can arise if other vehicles are in the blind spot. The driver can only identify the danger if he is being particularly cautious. The radar sensors of the lane change warning detect other vehicles on the neighboring driving lane up to around the centre of your own vehicle.
Brief component description
The following components are described for the lane change warning (SWW):
Assist systems operating facility
The lane change warning is switched on and off using the button in the control panel for driver assist systems.
The control panel is connected via the local interconnect network (LIN) bus to the footwell module (FRM). A bus signal from the FRM to the control unit for Integrated Chassis Management (ICM) informs regarding actuation of the button. The ICM control unit only allows the lane change warning to be enabled if the system is operating trouble-free. Only then is there positive confirmation by means of a bus signal to the footwell module (FRM) to activate the function indicator light of the button. If there is a fault in the system, the function indicator light remains switched off despite keystroke. This enables the driver to see that the lane change warning is no longer available.
SWW: Master control unit for lane change warning
The SWW control unit of the lane change warning (SWW) is simultaneously a radar sensor and a control unit. The control unit is installed in the rear right above the bumper bracket. From the outside, the radar sensor is not visible, rather it is covered by the bumper.
Only the right-hand radar sensor has a control unit address as well as a diagnosis address, thus making it a control unit.
The purpose of the radar sensor is to generate and send the radar waves. There is an integrated receive circuit. Signals are sent and received across a flat aerial.
The mounts of the radar sensors cannot be adjusted mechanically. Instead of adjusting the radar sensors mechanically (in the same way as e.g. the long-range sensor of the active cruise control), a correction angle must be stored via diagnosis.
Lane change warning, slave
The slave of the lane change warning (SWW) is exclusively a radar sensor and not a control unit. However, this radar sensor has a programmable memory and a separate processor. The radar sensor is installed in the rear left above the bumper support. From the outside, the radar sensor is not visible, rather it is covered by the bumper..
The purpose of the radar sensor is to generate and send the radar waves. There is an integrated receive circuit. Signals are sent and received across a flat aerial.
The mounts of the radar sensors cannot be adjusted mechanically. Instead of adjusting the radar sensors mechanically (in the same way as e.g. the long-range sensor of the active cruise control), a correction angle must be stored via diagnosis.
The left-hand radar sensor has different mounting points, which means it cannot be confused with the right-hand radar sensor.
Warning lamp in the exterior mirror
Both the left-hand and right-hand exterior mirrors contain a triangular warning lamp. The warning lamp can be activated with varying intensity. The control unit for Integrated Chassis Management (ICM) sends a request together with the required intensity to the footwell module (FRM). The request to the electronics of each exterior mirror is forwarded via LIN bus. Pulse-width modulated activation lights up the LEDs of the warning lamps.
When the turn indicator is set while a vehicle is in the critical range at the rear, the warning lamp flashes in the mirror housing (different intensity).
The lane change warning can issue a warning as of approx. 50 km/h.
Vibration actuator in the steering wheel
The vibration actuator is fitted in the spoke of the steering wheel. The vibration actuator has the task of causing the steering wheel to vibrate. The driver assistance systems 'lane departure warning' and 'lane change warning' use this vibration to warn the driver regarding dangerous situations.
The steering wheel module also housed inside the steering wheel activates the vibration actuator. The request for activation of the vibration actuator is sent by the Integrated Chassis Management (ICM) across the FlexRay to the steering column switch cluster (SZL). The SZL forwards this request across the LIN bus to the steering wheel module.
When the turn indicator is set while a vehicle is in the critical range at the rear, the steering wheel vibrates.
Alongside the lane change warning, the lane departure warning (KAFAS control unit) also uses the vibration actuator to generate a warning signal for the driver. The systems use different vibration amplitudes. The co-ordination for activation of the vibration actuator is integrated in the ICM control unit.
System functions
The following system functions are described:
- Functional networking
- Detecting road users
- Determining necessity for a warning
- System limits
Functional networking
A complex system network with distributed functions in other control units is necessary for implementation of the lane change warning. The following graphic shows the system network.
Detecting road users
Both radar sensors (master controller and slave) assume this function for the most part independently of one another each in its own detection range. First of all the position of the detected road user in the longitudinal and lateral directions is ascertained.
Building on this, the road users are assigned to a driving lane. Here, a distinction is made between the driving lane of the vehicle itself, the neighboring driving lane on the left or right and driving lanes that are further away. If road users are in the "lane change zone", the approach speeds in relation to the vehicle are detected. If a road user is in the area of the blind spot, it is already sufficient to detect their presence. The exact position or speed is not decisive for a warning.
Determining necessity for a warning
The necessity for a warning is determined by the master control unit for lane change warning (SWW). Here, the master control unit uses both the data regarding the road users it determined itself and that of the slave.
The gap (in longitudinal direction) and approach speed are used to calculate the time remaining before a lane change is aborted. If this time falls short of a threshold value for at least one of the detected road users, a decision is made that there is a necessity for a warning. The presence of a road user in the blind spot immediately leads to the necessity for a warning.
The necessity for a warning is suppressed if the master control unit receives information from the trailer module that a trailer is hitched. The body of a trailer limits the pickup range of the radar sensors excessively.
The result, i.e. whether a there is necessity for a warning or not, its sent by the master control unit to the ICM control unit.
System limits
NOTICE: Personal responsibility.
The system is no substitute for your personal appraisal of the traffic situation.
In the following sample situations, the function can be restricted:
- soiled or frozen bumper
- labels are stuck on the bumper
- trailer towing
In the event of restricted function, a Check Control message is displayed.
Notes for Service department
General notes
A calibration of the radar sensors is not necessary. If a radar sensor is replaced or work is performed on its mounting, a service function must be executed. This stores a correction angle in the radar sensors.
Diagnosis instructions
NOTICE: Follow the instructions for service functions.
The diagnosis system provides the following service functions for the lane change warning:
- Commissioning SWW sensor system (= lane change warning)
Path: Service functions > Chassis and suspension > Integrated Chassis Management
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.