Safety system and BYTEFLIGHT bus General functional description

The safety system involves the following functions:

• Electronic control of the fuel pump and fuel cutoff in an emergency
  
• Emergency call
  
• Battery terminal isolation
  
• Airbag activation
  
• Seat belts
  
• Headrests
  
• Seat occupancy detection.
  

The individual functions are specified in the relevant functional descriptions.

Brief description of components

BYTEFLIGHT bus system and star coupler SIM

The BYTEFLIGHT (fibre-optic cable) bus system has a star-shaped structure. The individual satellites (= control units with/without sensors) are interconnected across a star coupler by means of fibre-optic cables. The star coupler in the BYTEFLIGHT bus system is the SIM (Safety Information Module).

Satellites/control units

There is a transmission and a reception module (transmitter and receiver) as a unit in each satellite for connecting to the BYTEFLIGHT bus. The unit has an integrated transmit and receive diode.

The individual control units are described at the end of this functional description.

Sensors

The safety system uses data from internal and external sensors.

• Internal sensors: fitted in the BYTEFLIGHT control units, e.g. acceleration sensors
  
• External sensors: fitted outside the BYTEFLIGHT control units, e.g. belt buckle switch
  

The individual sensors are described at the end of this functional description.

Main functions

Self test

Self test on switching on terminal R: a self test is run when terminal R is switched on. This self test takes a maximum of approx. 10 seconds. The entire safety system is checked during this self-diagnosis phase.

• During this self test, the safety system cannot be activated.
  
• It is not possible to code and erase the fault memory.
  
• The AWL (airbag warning lamp) lights up.
  

Fault detected in the system: if the SIM (Safety Information Module) detects a current fault or a stored fault during this self test,

• the fault is stored in the fault code memory.
  
• If there is currently a major fault or a BYTEFLIGHT control unit is disconnected, the self test takes a maximum of approx. 1 minute.
  
• The AWL remains on after the 10 seconds if a fault is detected.
  

System without faults: if no fault is detected in the system, the AWL (airbag warning lamp) goes out again.

The safety system assumes standby mode as soon as the self test is completed.

Monitoring during vehicle operation: during vehicle operation, the individual satellites continuously monitor themselves. Here, the following checks are performed:

• Check of the flash memory
  
• Check of the safety-related bus messages
  

Activating the trigger circuits

In the event of an accident, the various acceleration sensors register the longitudinal and transversal deceleration values. In addition, pressure changes in the side doors can be measured by the STVL (satellite, door, front left) and the STVR (satellite, door, front right).

Occupants are detected by

• the seat occupancy recognition of the front seats: the satellites SSFA (satellite, driver's seat) and SSBF (satellite, passenger's seat) register the seat occupancy condition of the driver and the passenger.
  
• the seat occupancy recognition of the rear seats: in the case of the special equipment ”side airbag for rear seat passengers, incl. head airbag and electrically extendable outer headrests”, the SSH (satellite, rear seat) registers the seat occupancy to the two outer rear seats.
  
• the seat belt buckle monitoring (country version USA): switches in the seat belt buckles for driver and passenger monitor the condition of the seat belt buckle. The switches detect whether the ”seat belt is buckled” or the ”seat belt is not buckled”. With the optional feature ”audible belt warning”, the seat belt buckle is only fitted on the driver's side.
  

Activation of the trigger circuits requires acceleration values, seat occupancy recognition, seat belt buckle monitoring etc. All the information is placed as a message on the BYTEFLIGHT bus and evaluated by the SIM (Safety Information Module). The SIM, as BYTEFLIGHT bus master, decodes on the basis of all the available sensor data when the BYTEFLIGHT bus is to be set into a triggerable state. This ”trigger mode” places all the actuators of the safety system in the triggerable state.

To trigger a priming stage, two fully separate and independent signal and decision paths are required: For triggering

• the ”trigger mode” must be set by the SIM on the BYTEFLIGHT bus and
  
• there must be activation of the satellite to be triggered according to specific algorithms in each case (from each satellite).
  

Number of trigger circuits with maximum vehicle equipment:

With maximum vehicle equipment, the safety system controls and monitors the following trigger circuits:

• Driver's airbag, stage 1 and stage 2
  
• Front passenger's airbag, stage 1 and stage 2
  
• Thorax airbag (side airbag), front left
  
• Thorax airbag (side airbag) front right
  
• Thorax airbag (side airbag) rear left
  
• Thorax airbag (side airbag) rear right
  
• Head air bag, front and rear left
  
• Head air bag, front and rear right
  
• Knee airbag, front left
  
• Knee airbag, front right
  
• Active headrest, driver
  
• Active headrest, passenger
  
• Seat belt tensioner, driver
  
• Seat belt tensioner, passenger
  
• Seatbelt tensioner, rear left
  
• Seatbelt tensioner, rear right
  
• Belt tension limiter, front left
  
• Belt tension limiter, front right
  
• Battery safety terminal
  

Self-diagnosis of trigger circuits

The trigger circuits are checked

• during the self test with terminal R ON and
  
• while driving
  

Faults are indicated via the AWL (airbag warning lamp).

AWL and check control messages

The individual satellites send information regarding the control unit status to the SIM (Safety Information Module). The SIM collates this information. The SIM evaluates the information and correspondingly activates

• the AWL (airbag warning lamp).
  
• the check control messages in the information display of the instrument cluster. The generated display information for the check control is transferred by the SIM in cycles to the instrument cluster.
  

In the event of a fault:

• If the bus communication to the individual satellites is interrupted, messages are generated in the SIM. This is also the case during the self test.
  
• If the instrument cluster receives no display information for a period of 2 seconds, the AWL (airbag warning lamp) is activated.
  

SIM Output Voltage (UISIS)

The specified range for the power supply (UISIS) from the safety information module to the satellites is: 9 V - 11 V. The SIM switches off the power supply to individual satellites after about 4 seconds if

• the bus communication is disrupted (e.g. fibre-optic cable defective) or
  
• the leads to the power supply are defective.
  

If a satellite is unplugged, the power supply from the SIM to that satellite is thus also switched off. In order to be able to measure that output voltage from the SIM, the output must first be activated.

Example: output voltage (UISIS) from SIM is to be measured. The following procedure must be used:

• Terminal 15 On, i.e. ignition on
  
• for voltage measurement (UISIS), connect adapter to SIM
  
• switch to 'Control Unit Functions' SIM Safety Information Module
  
• Component activation: activate UISIS and light (diodes) (activation for 4 seconds)
  
• Measure voltage
  

Fault memory

The following additional information regarding the individual fault code memory entries can be obtained:

• Fault occurred at t > 1 min (i.e. a time greater than 1 minute)
  
• Fault occurred at 1 s < t < 1 min (i.e. a time between 1 second and one minute)
  
• Fault occurred at 0 s < t < 1 s (i.e. a time between 0 and 1 second)
  
• Fault start system time, e.g. 5.34 h
  
• Fault end system time, e.g. 5.38 h
  

The first three additional items of information can also occur as a combination. In the BYTEFLIGHT system, there is a uniform system time for all participants (slaves). On production of the vehicle, this system time is started by means of a diagnosis command. In the above example, the fault occurred for 0.04 hours.

Fault symptom: Airbag warning lamp (AWL) lights up, but there is no fault code memory entry

If the fault code memory is deleted after work on the vehicle, it can occur that the AWL lights up, but no fault is stored in the fault code memory of the BYTEFLIGHT control units. Even after ignition off and ignition on, the AWL does not go out and there is no fault code memory entry. The following procedure is required if this occurs:

• Ignition Off
  
• Let the vehicle ”sleep” (start/stop button no longer lights up)
  
• Ignition on
  
• Run a quick test
  

Following this, information on the fault should be available in the BYTEFLIGHT control units.

Control unit functions

In the test programs, the following instructions are given for certain faults:

1. Switch to 'Control Unit Functions' and perform the following steps:
   
2. Satellite: Erase fault memory
   
3. SIM Safety Information Module: Component activation: start self test
   
4. SIM Safety Information Module: Diagnosis request: observe end of self test
   
5. Satellite: read fault code memory
   

Note regarding 2.: switch to the control unit function of the relevant satellite and erase the fault memory.

Note regarding 3.: switch to the control unit function of the Safety Information Module. Under 'Component activation', start the self test (the self test is a test of the overall safety system). This operation is necessary so that any faults currently present are stored!

Note regarding 4.: switch to the control unit function of the Safety Information Module. Under diagnosis requests, observe end of self test (after self test ended, continue with 5.)

Note regarding 5.: switch to the control unit function of the relevant satellite and read the fault code memory.

Service functions

Notes on safety

In all cases, only perform work on the fuel pump with the ignition off!

All work on the airbags must be carried out with the battery disconnected!

Connect and disconnect all BYTEFLIGHT control units, sensors and generators only with the battery disconnected!

If a fibre-optic cable on the BYTEFLIGHT bus has to be repaired, it must be borne in mind that there may only be one join between the Safety Information Module (SIM) and a satellite. For this reason, no repairs may be performed on the fibre-optic cable between the SIM and the door satellites (STVL and STVR), as there is already a join with the door connector. In the case of a defect, the fibre-optic cable must be replaced!

Code all BYTEFLIGHT control units before initial start-up: the control units (satellites) contain vehicle-specific data!

Overview of the sensors and satellites (control units) in the safety system

Sensors

The safety system works with the data from a number of sensors. However, only the belt buckle switches and the sensor mats in the seats are external sensors. All other sensors are integrated in the relevant control units.

Control units on the BYTEFLIGHT bus

The safety system works with a number of control units, also referred to as ”satellites”. In part, the sensors are fitted in the satellites. However, the satellites also process data from external sensors. The BYTEFLIGHT actuators are activated on the basis of the information collected by the control units.