Pre-Safe (R), Function - GF91.40-P-0001GW

Model 463 (except 463.342) 

as of model year 2019 

Courtesy of MERCEDES-BENZ USA

Block diagram 

Function requirements, general 

• Circuit 15 ON
• No overvoltage or undervoltage

The electronic ignition lock control unit transmits the status of circuit 15 to the ESP® control unit via the suspension FlexRay.

• Function sequence for reversible tensioning retraction 
• Function sequence for seat belt adaptation 
• Function sequence for adjusting the seat contour (with code PA9 (Active Multicontour Seat Package)) 
• Function sequence for front passenger seat positioning 

PRE-SAFE®, general 

The preventive occupant protection system PRE-SAFE® detects a potential risk of accident in advance on the basis of critical driving situations. If necessary, functions can be activated as a precaution that reduce the risk of injury to the vehicle occupants. In order to do this, PRE-SAFE® permanently evaluates sensor data from systems such as the Electronic Stability Program (ESP®) and the driver assistance systems and can therefore, for example, detect excessive understeer or oversteer and emergency braking. If a critical driving situation is recognized, corresponding measures can be started within fractions of a second. These measures allow the restraint systems to provide their full protective effect in the event of a collision.

The PRE-SAFE® function is controlled by the Electronic Stability Program control unit.

The PRE-SAFE function® includes the following subfunctions:

• Function sequence for sensing the vehicle condition 
• Function sequence for closing sliding roof (with code F15 (Sliding roof)) 
• Function sequence for closing side windows 
• Function sequence for display of fault messages 
• Function sequence for terminating PRE-SAFE® functions 

Function sequence for sensing the vehicle condition 

The current vehicle status is defined by the Electronic Stability Program control unit by evaluating the following variables:

• Wheel speed
• Natural dynamics of the vehicle (yaw rate, lateral acceleration and longitudinal acceleration)
• Steering angle

In vehicles with code EM4 (Driving Assistance Package), the ESP® control unit also evaluates active assistance system interventions and collision-critical warnings.

The Distance Pilot DISTRONIC controller unit (with code EM4 (Driving Assistance Package)) or the Active Brake Assist controller unit (except code EM4 (Driving Assistance Package)) transmits the corresponding signals to the ESP® control unit via the suspension FlexRay. The PRE-SAFE® system is triggered for the following scenarios:

• Emergency braking: Fast brake pedal operation, which indicates a startled response by the driver.
• Maximum full-stop braking: the driver's deceleration request is significantly higher than the physically possible vehicle deceleration (e. g. aquaplaning, ice or snow). Strong interventions by the anti-lock braking system (ABS)
• Strong oversteer: Swerving of vehicle rear area combined with strong ESP® stabilization interventions
• Strong understeer: Vehicle pushes for a certain time over the front wheels. Strong stabilization interventions by the ESP®
• Crosswind stabilization: Drifting from the specified lane, connected with strong ESP® stabilization interventions
• Critical steering movement: rapid steering movements at fast speed that indicate a startled response from the driver and imply that the driver is unable to cope with this situation.
• Secondary accident: Occurrence of another accident after an initial accident

Also in vehicles with CODE EM4 (Driving Assistance package):

• Powerful brake assistance through BAS PLUS: Powerful support of the brake application initiated by the driver upon detection of risk of collision in linear traffic based on radar-assisted evaluation of the surroundings
• Autonomous brake application by the PRE-SAFE® brake: Vehicle deceleration with detected risk of collision in linear traffic by the PRE-SAFE® brake based on radar-assisted evaluation of the surroundings
• Autonomous course correction by the Active Blind Spot Assist: Significant, course-correcting brake application in the event of a registered danger of a side collision with vehicles in the blind spot based on radar-assisted evaluation of the surroundings
• Collision object detection at front/rear/side: detection of an imminent collision based on radar-assisted evaluation of the surroundings

The activation threshold for the PRE-SAFE® functions is modified depending on the following variables:

• ESP® mode
• Transmission mode

The head unit transmits the request for the selected ESP® mode and the selected transmission mode via the user interface CAN, the electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit.

Additional function requirements, reversible emergency tensioning retraction 

• Front seat belt applied

The Supplemental Restraint System control unit reads in the status of the driver seat belt buckle switch and the front passenger seat belt buckle switch directly and transmits this via the user interface CAN to the reversible emergency tensioning retractors.

Function sequence for reversible tensioning retraction 

The reversible emergency tensioning retractors reduce any seat belt slack in hazardous situations by tensioning the front seat belts using an electric motor. The driver and the front passenger are held in position better in their seats in order to optimize the protective effect of the conventional restraint equipment. Depending on the situation, the seat belt is tightened with varying force and speed.

The Electronic Stability Program control unit transmits information about the PRE-SAFE® status and the PRE-SAFE® stage via the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN to the reversible emergency tensioning retractors. To tighten the seat belt, the respective reversible belt tensioner actuates an integrated actuator motor.

The reversible emergency tensioning retraction is completed with the end of the PRE-SAFE® situation. Abort conditions:

• Switching off circuit 15
• Opening the respective seat belt buckle
• Occurrence of a crash event

Once the PRE-SAFE® measure is complete or canceled, the seat belt is slackened again (unless a crash has occurred). The Supplemental Restraint System control unit transmits the crash signal via the user interface CAN to the reversible emergency tensioning retractors.

Additional function requirements for seat belt adjustment 

• Function activated in head unit
• PRE-SAFE® has not been activated
• "Engine running" or "Drivetrain operational" signal set

The head unit transmits the status of the seat belt adaptation function via the user interface CAN to the reversible emergency tensioning retractor.

The CDI control unit (diesel engine) or the ME-SFI [ME] control unit (gasoline engine) transmits the "Engine running" signal or the "Drivetrain operational" signal via the drive train CAN, the powertrain control unit, the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN to the reversible emergency tensioning retractor.

Function sequence for seat belt adaptation 

The seat belt adaptation function reduces the amount of seat belt slack by tensioning the seat belts of the driver and front passenger seats using an electric motor. The function is triggered when the seat belt is fastened. Insertion of the belt lock tongue of the seat belt into the seat belt buckle is recorded through the status of the respective seat belt buckle switch.

The Supplemental Restraint System control unit reads in the status of the driver seat belt buckle switch and the front passenger seat belt buckle switch directly and transmits this via the user interface CAN to the reversible emergency tensioning retractors. In order to tighten the seat belt, the respective reversible emergency tensioning retractor actuates an integrated actuator motor. The seat belt is thereby tightened at a constant speed until the seat belt slack has been reduced.

Additional function requirements for adjusting the seat contour (with code PA9 (Active Multicontour Seat Package)) 

• Respective seat belt fastened
• Pressure level of side inserts and lumbar support bladders not equal to PRE-SAFE® specified pressure

The Supplemental Restraint System control unit reads in the status of the driver seat belt buckle switch and the front passenger seat belt buckle switch directly and transmits this via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the left front multicontour seat control unit or the right front multicontour seat control unit.

Function sequence for adjusting the seat contour (with code PA! (Active Multicontour Seat Package)) 

In order to optimize the protective effect of the conventional restraint equipment, the seat contour is adjusted before a potential accident using PRE-SAFE®. The Electronic Stability Program control unit transmits information about the PRE-SAFE® status and the request for PRE-SAFE® adjustment via the chassis FlexRay, the electronic ignition lock control unit and the interior CAN to the multicontour seat control units. An active setting, if given, is interrupted.

The following settings are made:

• Inflating the side inserts (vehicle occupants are held in a central position in the seat)
• Deflating the lumbar support bladders (vehicle occupants sit lower in the seat)

The PRE-SAFE® adjustment is completed when the PRE-SAFE® specified pressure reaches into the side inserts and lumbar support bladders or at the end of the PRE-SAFE® situation. Abort conditions:

• Switching off circuit 15
• Opening the respective seat belt buckle
• Manual adjustment request
• Memory function adjustment request

After completion or cancellation of the PRE-SAFE® measures, the inflation status of the side inserts and the lumbar support bladders is returned to the respective initial status.

Additional function requirements for positioning the front passenger seat 

• Front passenger seat occupied
• Seat adjustment normalized
• Front passenger seat outside PRE-SAFE® target position

The Supplemental Restraint System control unit transmits the status of the front passenger seat occupied recognition via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the front passenger seat control unit.

Function sequence for front passenger seat positioning 

In order to optimize the protective effect of the conventional restraint | equipment, the front passenger seat is moved into a position that is favorable from a safety point of view before a potential accident. The ESP® control unit transmits information on the PRE-SAFE® status and I the request for PRE-SAFE® adjustment to the front passenger seat control unit via the suspension FlexRay, the electronic ignition lock control unit and the interior CAN. An active setting, if given, is interrupted.

Depending on the current seat position, the following adjustments are made:

• Backrest inclination
• Seat height
• Seat fore/aft position
• Seat inclination

The PRE-SAFE® adjustment is completed when the PRE-SAFE® target position of the front passenger seat is reached or at the end of the PRE-SAFE® situation.

Abort conditions:

• Switching off circuit 15
• Opening or inserting the seat belt buckle
• Occurrence of a crash event
• Manual adjustment request

After completion or cancellation of PRE-SAFE® measures, the front passenger seat does not automatically return into the default position, but has to be manually adjusted if necessary.

Seat adjustment if the front passenger is not wearing his/her seat belt::

The system moves the seat into a position that is adapted to the unsafe conditions. The supplemental restraint system control system reads in the status of the front passenger seat belt buckle switch directly and transmits this via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the front passenger seat control unit.

Additional function requirements for closing the sliding roof (with code F15 (Sliding roof)) 

• Sliding roof NORMALIZED
• Sliding roof opened further than PRE-SAFE® target position

Function sequence for closing sliding roof (with code F15 (Sliding roof)) 

Closing the sliding roof ensures that no objects can penetrate into the vehicle interior and no body parts (e.g. arms) of the vehicle occupants can protrude from the vehicle in the event of a potential accident (rollover). The sliding roof is completely closed by PRE-SAFE® if it is opened before the PRE-SAFE® measure in the lift direction. If the sliding roof is opened before the PRE-SAFE® measure in the sliding direction, it is closed apart from a residual gap.

The ESP® control unit transmits information on the PRE-SAFE® status and the request for PRE-SAFE® adjustment to the sliding roof control module via the suspension FlexRay, the electronic ignition lock control unit and the interior CAN. Any automatic movement or manual setting that is active is aborted. The automatic reversing function is active when the sliding roof is being closed. If required, the closing process is reversed.

The PRE-SAFE® adjustment is completed by reaching the PRE-SAFE® target position of the sliding roof. Abort conditions:

• Switching off circuit 15
• Manual adjustment request

After completion or cancellation of the PRE-SAFE® measure, the sliding roof does not move back to the default position independently but instead must be manually adjusted if necessary.

Additional function requirements for closing the side windows 

• Power windows normalized
• Side windows opened further than PRE-SAFE® target position

Function sequence for closing side windows 

Closing the side windows apart from a small gap is intended to ensure that no objects can penetrate into the vehicle interior and no body parts (e. g. arms) of the vehicle occupants can protrude from the vehicle in the event of a potential accident (rollover). This also allows the smoke particles generated by the pyrotechnical restraint equipment to disperse quickly.

The Electronic Stability Program control unit sends information about the PRE-SAFE® status and the request for PRE-SAFE® adjustment ' via the chassis FlexRay, electronic ignition lock control unit and interior CAN to the following control units:

• Left front door control unit
• Right front door control unit
• Left rear door control unit
• Right rear door control unit

Active window lowering (automatic) or a manual setting is aborted. The automatic reversing function is active when closing the side windows using PRE-SAFE®. If required, the closing process is reversed. PRE-SAFE® adjustment is terminated when the PRE-SAFE® target position of the side window is reached.

Abort conditions: 

• Switching off circuit 15
• Manual adjustment request

After completion or cancellation of the PRE-SAFE® measures, the side windows do not automatically return into the default position, but have to be manually adjusted if necessary.

Function sequence for display of fault messages 

If the reversible emergency tensioning retractors detect faults, appropriate messages are displayed in the display of the instrument cluster. Faults in other components that are involved in PRE-SAFE® are not displayed as PRE-SAFE® faults.

The reversible emergency tensioning retractors send the request to display a fault message over the user interface CAN to the instrument cluster.

Function sequence for terminating PRE-SAFE® functions 

The PRE-SAFE® function is deactivated as soon as the current situation is deemed to be no longer critical. For this purpose, the Electronic Stability Program control unit withdraws the request to trigger the PRE-SAFE® measures from the chassis FlexRay.

The reversible emergency tensioning retractors are equipped with a mechanical acceleration sensor, which locks the belt extension in the event of any vehicle deceleration of more than 0.3 g. For this reason, the belt may remain mechanically locked even when the reversible emergency tensioning retraction has been completed.

	Electrical function schematic for PRE-SAFE®		PE91.40-P-2051-97ZGA
	Overview of system components for PRE-SAFE (R)		GF91.40-P-9997GW