Part I

Crash Safety

Crash safety
The 4th generation ACSM ("Advanced Crash Safety Module") discharges the following functions:
- Detecting an accident situation that is critical for the occupants
- Activating the necessary restraint systems (selectively depending on the severity of the accident and accident type)

Brief component description
Descriptions of the following safety-system components are provided:

NOTICE: There are differences in the equipment of the safety system depending on the series, model, vehicle equipment and national-market version.

The following description does not go into detail about all possible equipment ranges of the safety system in dependence on the series, model, vehicle equipment, optional equipment and national-market version.

ACSM: Crash safety module
The Crash Safety Module (ACSM) is the control unit for the safety system. No sensors are installed in the Crash Safety Module.
The Crash Safety Module performs a self test after the ignition is switched on. During this time, the airbag indicator light lights up (approx. 3 to 5 seconds). The airbag indicator lamp goes out as soon as the safety system is ready for operation.
All gas generators and sensors of the safety system are connected directly to the Crash Safety Module. The Crash Safety Module evaluates the acceleration data (longitudinal and lateral acceleration) of the sensors and thus determines the direction and severity of the accident in a collision. Comprehensive tests are used to define triggering thresholds for all possible types of accident. This results in different trigger thresholds for activation of the various restraint systems (airbags, seatbelt tensioners, etc.). When an impact occurs the Crash Safety System decides whether deployment is required and which gas generators (belt tensioners, airbags, crash-active head restraints, etc.) must be activated. The Crash Safety Module also triggers the safety battery terminal.
The restraint systems are triggered only when 2 independent sensors detect the corresponding threshold. The Crash Safety Module sends a message to other bus users when the restraint systems are triggered. The individual control units execute various functions according to the severity of the accident. For example, the footwell module (FRM) or front electronic module (FEM) activates the interior lights and hazard warning flashers. The Crash Safety Module transmits a signal to the Combox over a direct wire. The Combox automatically initiates an emergency call which also includes the location of the vehicle.
When the restraint systems trigger, certain data are written to a read only memory in the Crash Safety Module.
The data is relevant to accident research (no access for service). After 3 crash signals, the data memory is full.
The airbag warning lamp lights up. The Crash Safety Module must be replaced.
For the seat belt warning, the signals of the belt buckle switch are picked up separately.
The crash safety module contains an ignition capacitor. If the power supply is interrupted in the event of an impact, the ignition capacitor serves as an energy reserve for the crash safety module.







Front door airbag sensor, left and front door airbag sensor, right
The 2 airbag sensors are pressure sensors. The airbag sensors are fitted in each of the inner door panels. The airbag sensor consists of the following components:
- Pressure sensor for detection of a side-on crash
- Electronic module for signal processing and for data interchange

If the door outer skin is pressed inwards in a side-on collision, the door interior is reduced in size. This increases the pressure in the door interior. This increase in pressure is measured by the pressure sensor. The measured pressure values are digitized in the electronic module. The electronic chip transmits a message to the Crash Safety Module (transmitted in cycles). The message is processed in the Crash Safety Module (ACSM).

Airbag sensors on left and right B-pillars
Airbag sensors are fitted on the left-hand and right-hand B-pillars at the bottom in the area of the sill. Each airbag sensor contains a lateral acceleration sensor and a longitudinal acceleration sensor. The longitudinal acceleration sensor detects frontal or rear-end collisions. The lateral acceleration sensor acceleration sensor detects a side impact.

Airbag front sensor left and right
Front airbag sensors are bolted onto the left-hand and right-hand brace of the front panel. The 2 front airbag sensors are longitudinal acceleration sensors. The sensors detect frontal or rear-end collisions.

Belt buckle switch
The belt buckle switches indicate whether the seat belts have been fastened or not. The seat belt buckle switches receive voltage from the Crash Safety Module (ACSM). The current consumption of the switch is the signal for the switch position (seat belt fastened or not fastened). The seat belt buckle switches are permanently monitored whenever power is present at Terminal 15 and the status is wake-up line ON.
Whether or not the belt tensioner on the front passenger side is activated depends on the status signal of the seat belt buckle switch (seat belt fastened or not fastened). If the seat belt is inserted in the seat belt buckle switch, the belt tensioner is also triggered, if needed (only with frontal or rear-end collision). If the front passenger seat is detected as occupied via the signals from the seat occupancy mat without the belt buckle switch sending a signal, a seat belt warning is issued.

Seat position sensor (US version)
According to the regulations of the FMVSS (Federal Motor Vehicle Safety Standard), a 5th percentile woman must be distinguished from a 50th percentile man on the drivers seat. The seating position sensor detects the airbag range designed for a person with regard to the seat adjustment in longitudinal direction.
The seating position sensor is a Hall sensor and it is supplied with voltage via the Crash Safety Module.
The signal of the seating position sensor also influences the delayed triggering of stage 2 of the inflator assembly (driver's airbag and front passenger airbag) as well as the ignition squib for opening the discharge hole. If the vehicle is equipped with a memory seat, the seat-position sensor is omitted.

Front passenger seat occupancy detection via seat-occupancy mat with pressure sensors (European version)
The front passenger seat occupancy detection detects whether the seat is occupied or not. The seat occupancy mat consists of conductors and pressure sensors. The Crash Safety Module receives and processes the signals from the pressure sensors.
The following graphic shows the seat-occupancy mat using example: F25.
The seat-occupancy mat is installed between the cover and foam insert of the seat.







The following graphic shows the seat-occupancy mat using example: F20.
The seat-occupancy mat is installed on the underside of the foam insert.







When a weight is placed on the seat, resistance in the seat occupancy mat changes. The seat is detected as not occupied up to a weight of approximately 12 kg (only applies if the seat-occupancy mat is installed between the cover and the foam insert of the seat). The seat occupancy detection function, however, also depends on the type of seat. e.g.: The material tension in a leather seat or a taut sports seat is already interpreted as pressure on the sensors. In such cases, a weight below 12 kg can trigger the "seat occupied" condition.
The signal is transmitted to the Crash Safety Module (ACSM) in a direct wire. The signal is only required for the seat belt warning. For example, if the passenger's seat is recognized as being occupied without the seat belt buckle switch sending a signal, a fasten belt warning will be emitted.

Switch for passenger's airbag deactivation (European version)
The switch setting is selected using the integral code in the remote-control unit or the ID transmitter. The indicator lamp for front-passenger airbag deactivation lights up when the switch is OFF.
In the switch position "OFF", the following airbags on the passenger's side are not deployed:
- Front passenger airbag
- Side airbag (in the armrest side section of the passengers seat)
- Crash-active head restraint
- Knee airbag (if present)

Front passenger seat occupancy detection via seat-occupancy mat with capacitive sensor system (US version)
According to the regulations of the NHTSA (National Highway Traffic Safety Administration), a small child in the child restraint system specifically designed for the purpose on the front passenger seat must be detected automatically. If the passenger's seat is classified as "occupied" by a child restraint system specifically designed for the purpose, the Crash Safety Module (ACSM) automatically disables the airbags on the passenger's side (passenger's airbag, side airbag, knee airbag). The indicator light for front passenger airbag deactivation lights up. The following graphic shows the seat-occupancy mat using example: F25.







The front passenger seat occupancy detection consists of a seat-occupancy mat with a capacitive sensor system. The occupancy of the front passenger seat is detected by measuring the resistance of the human body.
Classification of the occupancy status is based on the evaluation of the capacitive resistance. The electronic evaluation unit picks up the change and determines the corresponding status.
The airbags on the front-front passenger side are deactivated automatically when a small child is detected in the child restraint system provided for this purpose. The indicator light for front passenger airbag deactivation lights up. If a person of adequate size sitting correctly is detected, the airbags on the front passenger side are activated. The indicator light for the front passenger airbag deactivation does not light up.
The front passenger airbag could deactivate with a youth or adult seated in certain positions (indicator light for passenger airbag deactivation comes on). In these cases, the seat position must be changed until the indicator light for the front passenger airbag deactivation goes out (airbags on the front passenger side are activated). The electronic processing circuit relays status information to the Crash Safety Module in cyclical transmissions. Potential error conditions are stored in the Crash Safety Module's fault memory.
If the seat occupancy mat is defective, the airbags on the front passenger side are automatically disabled (front passenger airbag, knee airbag, side airbag). The indicator light for front passenger airbag deactivation lights up.

CAS: Car Access System
The CAS control unit provides input signals for terminal voltages (such as Terminal 15 wake-up wire ON). The CAS control unit supplies voltage to the Crash Safety Module (ACSM) (starting at Terminal 30B ON).

DME or DDE: Digital Motor Electronics and/or Digital Diesel Electronics
The DME or DDE deactivates the electric fuel pump when an airbag deploys. The Crash Safety Module (ACSM) transmits the command through the CAN bus. The DME or DDE is on the bus.

ICM: Integrated chassis management
The networking of the suspension control systems by the ICM control unit provides a hierarchical function structure of all software-based driving dynamics functions.
The ICM control unit provides the systems in the entire vehicle with the dynamic driving state in the form of signals (e.g. data such as lateral and longitudinal acceleration, yaw velocity). The ICM control unit transmits these signals to other stations on the bus in the form of bus signals.
In addition to the sensors governing the vehicle dynamics control, the ICM control unit also contains longitudinal and lateral acceleration sensors to detect impacts.
Two wires provide a direct connection between the ICM control unit and the Crash Safety Module (ACSM) for transmission of the sensor signals.
Depending on vehicle equipment and the national-market version, the ICM control unit may also include a vertical acceleration sensor and a yaw rate sensor. Sensor signals are employed for vehicle dynamics systems as well as for impact detection. For impact detection the ICM control unit relays the sensor signals directly to the Crash Safety Module via two wires.







JBE: Junction Box Electronics
The JBE controls the central locking drive units. In the event of an accident with the corresponding severity, the central-locking system is unlocked.

ZGM: Central gateway module
The Central Gateway Module links all main buses to one another. Examples of a main bus include the FlexRay, MOST, PT-CAN and K-CAN. This enables the Gateway function on the Central Gateway Module to exchange data between the various different bus systems.
When the diagnosis system is connected through the D-CAN (Diagnose-on-CAN), the central gateway module data requests from the diagnosis system to the internal buses. The response telegrams run through the process in the opposite direction.

FRM: Footwell module
The footwell module controls the interior lighting and exterior lighting. In the event of an accident with the corresponding severity, the interior lighting and hazard warning lights switch on automatically.

Front electronic module (FEM): Front electronic module
The front electronic module controls the interior lighting and exterior lighting. In the event of an accident with the corresponding severity, the interior lighting and hazard warning lights switch on automatically.
The FEM control unit provides input signals for terminal voltages (such as Terminal 15 wake-up wire ON). The FEM control unit supplies voltage to the Crash Safety Module (ACSM) (starting at Terminal 30B ON).

Instrument panel: Instrument panel
The instrument panel shows the visual seat belt warning and issues an acoustic seat belt warning. The Crash Safety Module (ACSM) controls the visual seat belt warning using a Check Control Message. The instrument cluster receives the status from the Crash Safety Module whenever the terminal status is Terminal 15 wake-up wire ON or higher. With the corresponding status, a visual and acoustic seat belt warning is issued as of terminal 15 On.
The instrument panel also contains the airbag indicator light. The PT-CAN (Powertrain CAN) connects the instrument cluster to the Crash Safety Module.

CBX-MEDIA and CBX-ECALL: Combox multimedia and Combox emergency call
The Crash Safety Module (ACSM) responds to accidents beyond a specified severity by transmitting a signal over a data wire and to the Combox. The Combox automatically initiates an emergency call which also contains the location of the vehicle. With High equipment, the Combox consists of 2 components:
- Main board: Combox multimedia (CBX-MEDIA)
- Emergency call printed circuit board: Combox emergency call (CBX-ECALL)

In principle, these are 2 separate control units in one housing. These two control units also respond during the vehicle test in the diagnosis.
The high equipment version of the Combox is the only version with telematics capability (automatic emergency call).

Driver's airbag and front passenger airbag
The driver's airbag and front passenger airbag reduce the risk of head or chest injuries to the occupants in the case of a head-on collision. The driver airbag is located under the centre pad on the steering wheel. The front passenger airbag is built into the dashboard above the glove box.

Side airbag
The side airbags reduce the risk of injuries to the occupants in the lap or torso area in the event of a side-on collision. The side airbag are fitted in the armrest side sections of the front seats.

Crash active headrest
The crash-active head restraint is available for the driver's seat and front passenger seat.
On activation, the crash-active head restraint reduces the distance between the head restraint and head in order to reduce the load on the cervical vertebrae during a rear-end collision.

Head airbag
The head airbag prevents direct contact of the head against the side structure or an object entering the vehicle.
The head airbag stretches continuously at head height from the A-pillar to the C-pillar.
The shape and stability of the head airbag are retained for several seconds after deployment. The head airbag deflates more slowly than the front and side airbags. thus providing longer protection for the head in lateral rollover situations.
A head airbag is installed on the driver's side and on the front passenger side.

Knee airbag
When triggered, the knee airbag provides support for the knee if the front passenger is not wearing a seat belt. This initiates controlled forward displacement of the upper body. The upper body is cushioned by the respective airbag (driver's airbag or front passenger airbag).

Seatbelt tensioners for driver belt and passenger belt
As a rule, the seat belt does not fully tighten around the body. The so-called "belt slack" of the seat belt ensures that the occupants can move comfortably to an adequate degree. In the event of a collision, the pyrotechnic seatbelt tensioner pulls the belt buckle a number of centimeters downwards (bear the national version in mind), thus pulling the seat belt tight into the occupant's shoulder and pelvis.

Retractor tensioners for driver's seat belt and passenger belt
The effect of the reel tensioners is that in the event of a collision the occupants' shoulder region is fixed more strongly on the seat. The reel tensioner is connected to the reel mechanism. When the reel tensioner triggers, the seat belt is reeled in, pulling it taut.

Anchor fitting tensioner
The end fitting pretensioner prevents the driver's pelvis moving too far forward in the event a head-on or rear-end collision. The end fitting pretensioner is installed in addition to the seat belt tensioner on the driver's seat. In principle, the end fitting pretensioner functions in the same way as a seat belt tensioner.

REMAFA resp. REMABF: Reversible electromotive automatic reel, left and right
After evaluation of various signals and messages, the control unit recognizes whether the seat belt has to be pretensioned.
The reversible electromotive automatic reel system includes the following functions:
- Minimization of belt slack (the seat belt lies optimally against the driver's resp. front passenger's body)
- Stabilization of the seat position in a critical driving situation or in the event of a possible accident (pretensioning of the seat belt for optimizing the restraint system)

The reversible electromotive automatic reel consists of a automatic reel, electric motor with gearbox and an integrated control unit. The control unit is a bus user on the PT-CAN. After evaluation of various signals and messages, the control unit recognizes whether the seat belt has to be pretensioned. For example, the belt slack is thus removed after buckling up depending on the speed signal.
When a seat belt is put on, the control unit activates the respective reversible electromotive automatic reel one time over a specific period. Above an encodable driving speed (currently 10 Km/h), the seat belt strap is rolled up by the drive thus removing the belt slack.
In critical driving situations or in the event of a possible accident, the control unit also activates the drive. An algorithm calculates the driving condition and can issue the request for belt tensioning. The duration is set in such a way that the drive is activated by the control unit until a collision occurs or until a critical driving situation ends.
For calculating whether a critical driving situation exists, for example, vehicle oversteering, both control units (REMAFA and REMABF) use the data from the following systems:
- Integrated chassis management
The ICM control unit provides the systems in the entire vehicle with the dynamic driving state in the form of signals (e.g. data such as lateral and longitudinal acceleration, yaw rate).

- Dynamic Stability Control
The DSC control unit supplies information about brake pressure, for example.

- Crash safety module
The Crash Safety Module (ACSM) sends a message with the status of the seat belt buckle switches.
The request for tensioning the seat belt occurs from the Crash Safety Module (ACSM).

- Camera-based driver assistance systems
The camera-based driver support systems (KAFAS) supply the signals of the lane departure warning and object detection. The request for tensioning the seat belt occurs through the camera-based driver support system.

- Active cruise control
The Active Cruise Control (ACC) processes the signals about distance and speed about objects moving away from the vehicle in front of the vehicle and sends these to the Integrated Chassis
away from the vehicle in front of the vehicle and sends these to the Integrated Chassis Management (ICM). The request for tensioning the seat belt is sent via the PT-CAN to the respective reversible electromotive automatic reel (REMAFA and REMABF) via the Integrated Chassis Management.

A failure of a control unit has no effect on the restraining function of the seat belt.

Seat belt force limiter
The seat belts are the primary restraint system for all occupants. To minimize the force in the chest area of the occupants in the event of a severe frontal collision, the front seat belts are equipped as-series standard with belt tension limiters. The mechanical belt tension limiters ensure that the seatbelt strap has a defined flexibility as of a certain force. The danger of injury due to belt forces exerted on the body is reduced.

Adaptive belt force limiter, front left and front right
The pyrotechnic belt force limiter minimizes the load on the upper torso of the front-seat occupants in the event of a severe head-on collision. The danger of injury due to belt forces exerted on the body is reduced.
There are 2 torsion shafts installed in the automatic\n reel. The torsion shafts are intermeshed. Up to a certain load, the belt force is specifically limited by the two torsion shafts. From a certain load, a gas generator is used to decouple the torsion shafts. Only one of the torsion shafts is connected to the seat belt. This allows the belt force to be smoothly limited for the entire duration of the crash.

Safety battery terminal
Depending on the severity of the accident, the safety battery terminal may disconnect the starter motor, the alternator and the remote battery terminal from the battery. This prevents the risk of electrical short-circuits in a serious accident.
Even if the safety battery terminal is disconnected, the system ensures that voltage continues to be supplied to all safety-relevant electrical equipment, such as the hazard warning flashers, interior lamps and phone.

Airbag control lamp
The airbag indicator lamp indicates the safety system's current operational status. The instrument cluster's airbag indicator lamp is controlled by the Crash Safety Module (ACSM) over the PT-CAN.

Seat belt warning lamp
The seat belt warning lamp is the visual seat belt warning. The visual seat belt warning tells the occupants to fasten their seat belts. The visual seat belt warning is started as of terminal 15 On (bear national version in mind).
The visual seat belt warning is displayed as follows:
- The seat belt warning lamp lights up in the instrument panel
- Check Control message in the instrument panel

Indicator lamp for passenger airbag deactivation
When the indicator lamp for front passenger airbag deactivation is lit, this means that the following passenger-side airbags have been deactivated:
- Front passenger airbag
- Side airbag (in the armrest side section of the passengers seat)
- Crash-active head restraint
- Knee airbag (if present)

The Crash Safety Module (ACSM) continuously monitors the indicator lamp for the passenger airbag deactivation.
A fault in the voltage supply or a defective light is stored in the fault memory of the Crash Safety Module. If this occurs, the airbag warning lamp is switched on.

Fuel pump
Depending on the severity of the accident, the flow of fuel is also interrupted. The DME or DDE switches the electric fuel pump off in response to commands from the Crash Safety Module.

System functions
Descriptions of the following safety system functions are provided:
- Functional networking
- Self-test
- Impact detection
- Activating the safety system
- Message to other control units
- Visual and audible seat belt warning