Camera-based Driver Support Systems KAFAS

In the 7 series G11/G12, depending on the options fitted, various camera-based systems are available. Technical implementation is released with camera in the mirror base and control unit, the KAFAS control unit.
The most important display function of the camera-based driver assistance systems are as follow :

• ·         Lane departure warning
• ·         High-beam assistance (not permitted in Japan)
• ·         Speed limit (Speed limit info)
• ·         Collision warning
• ·         Overtaking ban
• ·         Urban traffic accident prevention
• ·         Preventive pedestrian protection
• ·         Traffic jam assistant

The following components for camera-based driver support systems (KAFAS) are described :

·         Light operating unit, turn signal/high beam switch

The high beam assistant is switch-ON and OFF at the turn signal/high beam switch. To do this, the light switch must be in the automatic driving lights control or low beam headlight position.

An additional prerequisite is that the low beam headlights are switch ON due to sufficient dark. For vehicles without automatic driving lights control, the high beam assistant can also be activated for brightness. The high-beam assistant switches on the low beam headlights based on the ambient brightness. The lane departure warning and collision warning are switched ON and OFF using the button in the driver assistance system operating facility. The driver assistance system operating is connected to the BDC via Local interconnect network bus. A bus signal from the BDC to the KAFAS control unit informs it that the button has been pressed. The central control unit for all video-based functions is the optional equipment system control unit (SAS).

The SAS control unit only allows the lane departure warning to be switched ON if the system is operating trouble-free. Only then is there positive confirmation by means of a bus signal to the Body Domain Controller to activate the button function indicator light. If there is fault in the system, the function indicator light remains switched off despite keystroke.  This allows the driver to see that the lane departure warning is not available.

The driver assistance system operating facility is located in the centre console by hazard warning button.

·         KAFAS control unit with stereo camera

The KAFAS control unit is now installed in front of the roof function centre on the roof liner. The stereo camera is integrated in the KAFAS control unit. The light spots, light colors and light intensities picked up by the stereo camera are evaluated by the KAFAS control unit. The evaluation by the KAFAS control unit results in switch on recommendation or switch off recommendation. The stereo camera monitors the area in front of vehicle. The video camera records the roadway up to approximately 40 meters in front of the vehicle and up to approximately 5 meters to the right and left at the sides of vehicle. The image data is evaluated by the KAFAS control unit. The stereo camera has 2 lenses. This means that a three-dimensional image can be recorded.

The following elements are detected :

• Object (vehicles, pedestrians, generic objects)
• Free space in front of the vehicle
• Preview of the course of the road
• Road markings
• Road signs

Tyre Pressure Control

Many types of tyre damage is indicated by a loss of tyre pressure. Tyre pressure control warns the driver when tyre pressure is lost on one or more wheels. This can also prevent preliminary damaged to a tyre.
Tyre pressure control is a system for monitoring the tyre pressure when driving. Tyre pressure control does not mean that the driver does not need to check the tyre pressure regularly. Initialization of the tyre pressure monitoring system must be triggered following each change in tyre inflation pressure as well as after every tyre changes.

Component description
The tyre pressure monitoring system functionality has now been integrated in the Dynamic Stability Control (DSC) system.
The remote control receiver reveives the radio signals from the wheel electronics. The remote control receiver is connected via LIN bus to the Body Domain Controller. The BDC forwards the signals via the bus connection to the DSC control unit.
The DSC control unit processes the messages transmitted by the wheel electronics. Above a speed of 20 - 30 km/h, the following messages are sent by the electronics on each wheel:

• Tyre pressure
• Tyre air temperature
• Remaining service life of the battery
• Data from the acceleration sensor and Identification Feature (ID) of the wheel electronics
• Transmission mode (passive, standby, learning)

The DSC control unit transmits information to the instrument cluster and headunit. The instrument cluster indicates tyre pressure loss via a warning and indicator light and issues a Check Control Message.

Wheel electronics
In all wheels, wheel electronics systems are installed in the wheel drop centre. The wheel electronics systems are bolted onto the filling valves (made of metals). All wheels electronics systems are common parts. The wheel electronics monitor the actual temperature in the tyre.
Each wheel electronics unit incorporated an acceleration sensor. The acceleration sensor recognizes whether the wheel is stationary or rotating. When the wheels are stationary the remote receiver does not transmit messages to the DSC. The wheel electronics are in their passive state. This extends the service life of the batteries in the wheel electronics. Once the vehicle reaches 30 km/h the wheel electronics switch to their standby mode. The wheel electronics start to transmit in defined cycles.
The wheel electronics measure the tyre inflation pressure and temperature at regular periodic intervals. The remote receiver relays these monitored data from the tyre to the DSC in periodic cycles.
The DSC control unit relies on the identification number that accompanies the transmissions to assign the information to individual wheels.

Wheel assignment
During the wheel assignment identification process the wheel electronics are in the learning mode. Wheel rotation generates centrifugal force. The acceleration sensor starts to recognize this centrifugal force at a vehicle speed of approximately 30 km/h. The acceleration sensor relies on the earth's gravitational force to identify the wheel electronics' vertical position (12 o'clock).
This position is needed for the learning mode.
In the learning mode the DSC identifies the positions of the four individual wheels with assistance from wheel sensors.

Remote control receiver
The messages of the wheel electronics are transmitted via high-frequency transmission path (433 Mhz) to the remote control receiver. The measuring cycle of the wheel electronics is 3 seconds. Transmission to the remote control receiver takes place every 30 seconds. The current status of the messages is forwarded on the LIN bus to the BDC. BDC control unit forwards the mesages via the Flexray to the DSC control unit. The DSC control unit evaluates the messages. 

Run Flat Indicator

Wheel-speed sensor failure

If no signal is received from one of the wheel-speed sensors, the RPA will switch to "inactive" mode after approximately 2 minutes. The RPA indicator and warning light lights up yellow. The fault is indicated with a check control message.
A fault is recorded in the fault memory of the RPA control unit. If the RPA is integrated into the DSC Dynamic Stability Control, a fault will be recorded in the DSC control unit.


Read off status of initialization phase
The status of the initialization phase can be displayed in the service functions for the control unit concerned (e.g. DSC control unit).

If a claim is entered due to the RPA not giving a warning on time, the status of the initialization phase can be displayed in service. The time of the last initialization is also displayed in service.

A warning can only be emitted in the speed range that have been calibrated by at least 67%.

Coolant Temperature Sensor

Depending on the engine, the coolant temperature sensor is installed at different locations. Observe the corresponding installation location. The coolant temperature sensor converts the temperature of the coolant and therefore of the engine oil into an electrical value (resistance). To do this, a resistance with negative temperature coefficient (NTC) is used. The coolant temperature is the measured variable for the following calculations, for example: Fuel injection rate and nominal idle speed.


Functional description


A temperature-dependent electrical resistor is used for temperature sensing. The circuit contains a voltage divider where the resistance can be measured depending on the coolant temperature sensor, whose resistance value drops when the temperature increases.


The resistance is temperature-dependent and varies between 217 kilo ohm and 37 ohm, which corresponds to a temperature of -55 to 155 degree C.


The resistance is dependent on the coolant temperature. A table that specifies the temperature associated with each resistance value is stored in the engine control. This compensates for the non-linear relationship between resistance and temperature.


Failure of the component


If the coolant temperature sensor fails, the following behavior is to be expected:

• Fault entry in the engine control unit
• Emergency operation with substitute value

Alternator

The alternator exchanges data with the engine control unit using a serial data interface. The alternator provides the engine control unit with information, e.g type and manufacturer. This enables alternator-specific information to be processed inside the engine control unit and adapts the control of the alternator to the installed alternator type.

With Intelligent Generator Control IGR, the alternator voltage is correspondingly more frequently in the low voltage range in order to achieve a better battery charge.

Functional Description

The alternator maintains the desired level of vehicle voltage. The alternator also supplies all electrical consumer units during driving. The controller regulates the output voltage of the electrically excited alternator with uncontrolled rectifier by applying the excitation current.

For the alternator with serial data interface, the following functions are implemented in the engine control unit :

• Switching the alternator on and off on the basis of defined parameters
• Temperature-dependent maximum permitted power consumption of the alternator
• Calculation of the alternator input torque and the alternator current based on the parameters transmitted by the alternator regulator.
• Control of the reaction of the alternator with addition of high power consumers (load-response functions)
• Alternator diagnosis and diagnosis of the data line between alternator and engine control unit.
• Storage of any faults that occurs on the alternator in the fault memory of the engine control unit.

Failure of the component

The main function of the alternator is also ensured in the event of interruption of the communication between the alternator and engine control unit. The following fault causes are distinguish by the fault memory entries :

• Overheating function : The alternator is overloaded. For safety reasons, the alternator voltage is reduced until the alternator has cooled down again. That is a normal operating condition for the alternator.
• Mechanical fault  : There is mechanical block in the alternator or the belt drive is defective.
• Electrical fault  : Defect in the excitation power circuit (transistor, diode), open circuit in the excitation coil, faulty controller.
• Communication failure : Faulty cable between engine control unit and alternator.
• Incorrect type of alternator : Incorrect or non-approved alternator installed.

An interrupt or short circuit in the coils of the alternator can not be detected.

Airbag Sensors

Function

Owing to the differences in crash test requirements for ECE and US vehicles, the ACSM Advance Crash Safety Module sensor systems for the two versions also differ. The sensors detect and confirm front, side and rear impacts. Signals from the sensors are transmitted directly to the ACSM for processing.
The ACSM then determines the direction and intensity of the impact based on data relayed by the sensors. The thresholds must be exceeded at two separate sensors before a crash is recognised.

Safety

All work on the airbag must only be conducted with the battery disconnected. Connect and disconnect airbag control unit, sensors and gas generators only with the battery disconnected. The airbag control unit contains vehicle-specific data and must therefore encoded before start-up. Removal and installation in other vehicles is prohibited.

Aerial Diagnosis

Aerial diversity is a system that selects the aerial that has the best reception from aerials in the vehicle (max.4). This signal is reinforced in the aerial diversity and transmitted to the tuner. In the following, the tests preformed in the aerial diversity procedure are briefly described. Depending on the equipment, it is possible that aerial diversity is not fitted. In this case, the aerial is directly connected to the headunit via an aerial amplifier.

DC measurement

The DC measurement detects whether the aerial diversity is correctly connected to the tuner. Additionally, the corresponding fault code entries will also be evaluated during the procedure.
The diversity function and the aerial connection will be checked by means of the aerial self-diagnosis. However, these results are not always significant. In this case, it is necessary to consider the field strength of the transmitter that can be received.

Service mode

In the radio service mode, it is possible to display the quality and the field strength of the radio station already being received (not MASK and CCC). The values displayed are between 0 and 15.

• 15 corresponds to a very good reception
• 0 corresponds to a very bad reception

Proceed as follows to call up the service mode :

• Terminal 30g ON
• Switch off the radio
• Switch on the radio again
• Within 8s and for a duration of 8s, press the button for the manual search
• The radio switches into the Service mode.

 Evaluation

If the result of the aerial diversity self-diagnosis is OK, the field strength of the transmitter already received can be displayed in the procedure.
If an aerial has a noticeably weaker reception than the other aerials, the vehicle must be turned around by 90 degrees and the measurement taken again. If a weakness in the tolerance range continuous to occur, then at least one FM aerial is faulty. The faulty FM aerial must be checked.