PRE-SAFE function - GF91.40-P-0001GN

MODEL 166 as of model year 2016

MODEL 292

Fig 1: Pre-Safe Block Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general

Terminal 15 ON
No overvoltage or undervoltage
"Engine running" or "Drive train operational" signal set (except with seat belt adjustment function)

The electronic ignition lock control unit sends the status of circuit 15 via chassis CAN 1 to the Electronic Stability Program control unit and to the reversible emergency tensioning retractors.

The CDI control unit or the ME-SFI [ME] control unit (except model 166.063) sends the "Engine running" or "Drivetrain operational" signal over the chassis CAN 1 to the Electronic Stability Program control unit. On model 166.063, the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain operational" signal over the drive train CAN, powertrain control unit and chassis CAN 1 to the Electronic Stability Program control unit.

PRE-SAFE®, general

The preventive occupant protection system PRE-SAFE® can recognize critical driving situations in advance and activate various systems that reduce the risk of injury to the vehicle occupants as a precautionary measure if necessary. To do so, PRE-SAFE® permanently evaluates the sensor data from systems such as the Electronic Stability Program (ESP®) and the Brake Assist System PLUS (BAS PLUS), which allows it to recognize excessive understeer or oversteer and emergency braking, for example. If a critical driving situation is recognized, corresponding measures can be started within fractions of a second. These measures allow the seat belts and airbags 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 status
Function sequence for reversible tensioning retraction
Function sequence for seat belt adaptation
Function sequence for positioning the front passenger seat (with CODE P64 (Memory package))
Function sequence for adjustment of seat contour (with CODE 399 (Front multicontour seats with massage function))
Function sequence for closing side windows
Function sequence for closing sliding roof (with CODE 414 (Sliding roof)) or Panoramic sliding sunroof (with CODE 413 (Panoramic sliding sunroof))
Function sequence for display of fault messages
Function sequence for terminating PRE-SAFE® functions

Function sequence for sensing the vehicle status

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

Detailed information about the acquisition of these variables can be found in the separate ADAPTIVE BRAKE function description.

The Electronic Stability Program control unit also evaluates the following signals from different driver assistance systems:

Autonomous brake application:
The radar sensors control unit (with CODE 23P (Driving assistance package Plus)) transmits the "autonomous braking" signal via the chassis FlexRay, the chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit.
Collision-critical warning:
The COLLISION PREVENTION ASSIST controller unit (with CODE 258 (COLLISION PREVENTION ASSIST)) transmits the "Collision-critical warning" status via chassis CAN 1 to the Electronic Stability Program control unit.

The Electronic Stability Program control unit differentiates between the following critical driving statuses:

Emergency braking: Fast brake-pedal operation, which indicates a startled response by the driver.
Panic braking: The driver's deceleration request is significantly higher than the physically possible vehicle deceleration on a slippery road (e.g. aquaplaning, ice or snow). Strong interventions of the anti-lock braking system (ABS).
strong oversteer: Swerving of rear end combined with strong ESP® stabilization interventions.
Strong understeer: Vehicle pushes for a certain time over the front wheels. Strong ESP® stabilization interventions.
Critical steering movements: Rapid steering movements at high speeds (v > 140 km/h) that indicate a startled reaction from the driver, making it highly likely that the driver will not be able to cope with this situation.
Strong braking support by BAS PLUS (with CODE 23P (Driving assistance package Plus)): Strong support of brake application initiated by the driver in response to recognized threat of collision in longitudinal traffic based on a radar-supported assessment of the surroundings.
Autonomous braking by PRE-SAFE® brake (with CODE 23P (Driving assistance package Plus)): Deceleration of the vehicle in response to recognized threat of collision in longitudinal traffic by the PRE-SAFE® brake based on a radar-supported assessment of the surroundings.
Front collision object detection (with CODE 23P (Driving assistance package Plus)): Detection of an imminent frontal impact (under certain conditions) based on a radar-supported assessment of the surroundings.
Autonomous course correction through Active Blind Spot Assist (with CODE 237 (Active Blind Spot Assist)): Pronounced, course-correcting brake intervention with registered risk of a side collision with vehicles in blind spot based on a radar-supported assessment of the surroundings.

The triggering threshold for the PRE-SAFE® functions is increased if the ESP® was manually switched to passive via the ESP OFF button in the upper control panel control unit. The SAM control unit reads in the status of the ESP OFF button via battery sensor LIN and sends this via interior CAN, electronic ignition lock control unit and chassis CAN 1 to the Electronic Stability Program control unit.

Additional function requirements, reversible emergency tensioning retraction

Front seat belt applied

The Electronic Stability Program control unit sends information on the PRE-SAFE® status and on the PRE-SAFE® stage via chassis CAN 1 to the reversible emergency tensioning retractors. The supplemental restraint system control unit sends the crash signal via chassis CAN 1 to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates an integrated actuator motor.

Additional function requirements for seat belt adjustment

Function activated in instrument cluster
PRE-SAFE® has not been activated

The instrument cluster sends the status of the seat belt adjustment function via chassis CAN 2, electronic ignition lock control unit and chassis CAN 1 to the reversible emergency tensioning retractors.

Function sequence for seat belt adaptation

The seat belt adjustment function reduces the existing seat belt slack by tensioning the seat belts using an electric motor. The function is triggered when the belt lock tongue is inserted into the respective belt buckle. The insertion of the belt lock tongue of the seat belt into the belt buckle is recorded via the status of the respective belt buckle restraint system switch.

The supplemental restraint system control unit reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN 1 to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates an integrated actuator motor. This tightens the belt strap at a constant speed until the seat belt slack has been reduced.

Additional function requirements for positioning of the front passenger seat (with CODE P64 (Memory package))

Front passenger seat occupied
Seat adjustment normalized

The supplemental restraint system control unit sends the status of the front passenger seat occupied recognition via chassis CAN 1, electronic ignition lock control unit and interior CAN to the front passenger seat control unit.

Function sequence for positioning the front passenger seat (with CODE P64 (Memory package))

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 Electronic Stability Program control unit sends information about the PRE-SAFE® status and the request for PRE-SAFE® adjustment over the chassis CAN 1, electronic ignition lock control unit and interior CAN to the front passenger seat control unit. Any memory or manual setting that may be active is aborted.

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

Seat fore/aft position
Seat height
Seat inclination
Backrest inclination

The PRE-SAFE® setting continues until:

The target position is reached (front passenger seat in optimum position)
The impact occurs
End of PRE-SAFE® situation

The PRE-SAFE® adjustment of the front passenger seat can be canceled at any given time through manual adjustment requests. The front passenger seat does not automatically return into the position before the PRE-SAFE® situation, 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 respective belt buckle restraint system switch directly and sends this via chassis CAN 1, electronic ignition lock control unit and interior CAN to the front passenger seat control unit.

Detailed information about adjusting the front passenger seat can be found in the separate electrical seat adjustment function description.

Additional function requirements for adjustment of seat contour (with CODE 399 (Front multicontour seats with massage function))

Seat belt applied

The supplemental restraint system control system reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN 1, electronic ignition lock control unit and interior CAN to the multicontour seat control units.

Function sequence for adjustment of seat contour (with CODE 399 (Front multicontour seats with massage function))

In order to optimize the protective effect of the conventional restraint equipment, the seat contour of the driver and front passenger seat is adjusted by PRE-SAFE® before a potential accident. The Electronic Stability Program control unit sends information about the PRE-SAFE® status and the request for PRE-SAFE® adjustment via chassis CAN 1, electronic ignition lock control unit and interior CAN to the multicontour seat control units. Any memory or manual setting that may be active is aborted.

The following settings are made:

Inflating the side inserts (the driver and the front passenger are held in a central position in the seat)
Deflating the air cushions in the lumbar area (driver and front passenger sit lower down in their seats)

The PRE-SAFE® setting continues until:

Specified pressure reached in the side inserts
The impact occurs
End of PRE-SAFE® situation

The PRE-SAFE® setting of the seat contour can be canceled at any time by making manual adjustment requests. Following a PRE-SAFE® situation, the inflation status of the side inserts and the airbag in the lumbar area is returned to the respective initial status.

Detailed information about adjusting the seat contour can be found in the separate electric seats function description in the multicontour seat function.

Additional function requirements for closing the side windows

Power windows normalized

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 occupants can protrude from the vehicle in the event of a potential accident. 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 over the chassis CAN 1, 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

Any automatic opening or manual setting that is active is aborted. The automatic reversing function is active when closing the side windows using PRE-SAFE®. If required, the closing process is reversed. The PRE-SAFE® setting continues until:

The side windows reach the PRE-SAFE® position
The impact occurs

The closing of the respective side window by PRE-SAFE® can be interrupted at any time by manual adjustment requests. Following the PRE-SAFE® situation, the side windows must be manually moved back into the desired position.

Detailed information about controlling the side windows can be found in the separate power windows function description in the power windows function.

Additional function requirement for closing sliding roof (with CODE 414 (Sliding roof)) or Panoramic sliding sunroof (with CODE 413 (Panoramic sliding sunroof))

Sliding roof NORMALIZED

Function sequence for closing sliding roof (with CODE 414 (Sliding roof)) or Panoramic sliding sunroof (with CODE 413 (Panoramic sliding sunroof))

Closing the sliding roof apart from a small gap ensures that no objects can penetrate into the vehicle interior and no body parts (e.g. arms) of the occupants can protrude from the vehicle in the event of a potential accident. 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 chassis CAN 1, electronic ignition lock control unit and interior CAN to the panoramic sliding sunroof control unit in the panoramic sliding sunroof control module or to the sliding roof control module.

If closing is activated by PRE-SAFE® during a manual adjustment, the manual adjustment is completed first and then closing by PRE-SAFE® is carried out. If closing is activated by PRE-SAFE® during an automatic operation, the automatic operation is aborted and closing is carried out by PRE-SAFE®. The automatic reversing function is active when closing the roof using PRE-SAFE®. If required, the closing process is reversed.

The PRE-SAFE® setting continues until:

The roof reaches the PRE-SAFE® position
The impact occurs

Closing of the roof can be aborted at any time by means of manual adjustment requests. Following the PRE-SAFE® situation, the roof must be manually moved back into the desired position.

Detailed information about controlling the roof can be found in the separate sliding roof (with CODE 414 (Sliding roof)) and panoramic sliding sunroof (with CODE 413 (Panoramic sliding sunroof)) function descriptions.

Function sequence for display of fault messages

If the reversible emergency tensioning retractors detect faults, these are displayed in the multifunction 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 the fault message via chassis CAN 1, electronic ignition lock control unit and chassis CAN 2 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 obtains the information about the PRE-SAFE® status from the chassis CAN 1.

The adjustment of the front passenger seat is aborted. Closing of the side windows and the roof is not aborted. The automatic closing function continues until the PRE-SAFE® position has been reached. The reversible emergency tensioning retraction is released as soon as the vehicle acceleration has dropped below a value of a = 0.3 g.

The reversible emergency tensioning retractors are equipped with a mechanical acceleration sensor, which locks the belt extension in the event of any vehicle acceleration of a > 0.3 g. For this reason, the belt may remain mechanically locked even when the reversible emergency tensioning retraction has been completed. When there is a crash event that is detected by the supplemental restraint system control unit, all adjustments are immediately stopped.

Electrical function schematic, pre-safe	PE91.40-P-2051-97NBA
Overview of PRE-SAFE system components	GF91.40-P-9997GN