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

MODEL 218

Fig 1: Pre-Safe - Block Diagram

Courtesy of MERCEDES-BENZ USA

Up to 28.02.2013

Fig 2: Pre-Safe - Block Diagram

Courtesy of MERCEDES-BENZ USA

As of 01.03.2013

Function requirements, general

Terminal 15 ON
"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 to the Electronic Stability Program control unit via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to.

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain ready" signal to the Electronic Stability Program control unit via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013).

PRE-SAFE®, general

The PRE-SAFE® function is activated in critical situations, in other words in a potential accident situation. The goal is to create the most favorable conditions possible for the occupants by activating functions prior to the potential accident (preventive measures) in order minimize the consequences of the expected accident.

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 (275) Memory package for electrically adjustable front seats)
Function sequence for adjusting the seat contour (with code (432) Active multicontour seat)
Function sequence for closing side windows
Function sequence for closing the sliding roof (with code (414) Power glass tilting/sliding roof)
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 the following variables.

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

Detailed information about acquisition of these variables can be found in the separate function description "Adaptive Brake (ABR) function".

Additionally, the Electronic Stability Program control unit on vehicles up to 31.08.2014 with code (233) DISTRONIC PLUS, code (237) Active Blind Spot Assist or code (238) Active Lane Keeping Assist or as of 01.09.2014 with code (23P) Driving assistance package Plus evaluates the "autonomous brake application" signal. The video and radar sensor system control unit (up to 31.08.2014 with code (233) DISTRONIC PLUS, code (237) Active Blind Spot Assist or code (238) Active Lane Keeping Assist) sends the "autonomous brake application" signal via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the Electronic Stability Program control unit. The radar sensors control unit (as of 01.09.2014 with code (23P) Driving assistance package Plus) sends the "Autonomous brake application" signal via the chassis FlexRay, chassis gateway control unit, and chassis CAN 1 to the Electronic Stability Program control unit.

The Electronic Stability Program control unit differentiates the following driving states:

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 intense Electronic Stability Program (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 Brake Assist (BAS PLUS) (with code (233) DISTRONIC 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 (up to 31.08.2014 with code (233) DISTRONIC PLUS or as of 01.09.2014 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 the radar-supported assessment of the surroundings.
Front collision object detection (with code (233) DISTRONIC PLUS): Detection of a 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® has been manually switched to passive via the menu on the instrument cluster. On vehicles up to 28.02.2013, the instrument cluster sends the status of the ESP® to the Electronic Stability Program control unit via chassis CAN and on vehicles as of 01.03.2013 via chassis CAN 2, front SAM control unit and chassis CAN 1.

Additional function requirements, reversible emergency tensioning retraction

Seat belt applied

Function sequence for reversible tensioning retraction

The reversible emergency tensioning retractors reduce any seat belt slack in hazardous situations by tensioning the seat belts using an electric motor. The driver and the front passenger are held in position in order to optimize the protective effect of the conventional restraint equipment. Depending on the situation, the belt strap of the seat belt is tightened with varying force or speed. After the PRE-SAFE® measure, the belt strap of the seat belt is slackened again (unless a roll-over has occurred).

The Electronic Stability Program control unit sends information about the PRE-SAFE® status and the PRE-SAFE® stage via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the reversible emergency tensioning retractors. The Supplemental Restraint System control unit sends the crash signal via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor directly actuates the integrated front reversible emergency tensioning retractor actuator motor.

Additional function requirements for seat belt adjustment

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

On vehicles up to 28.02.2013, the instrument cluster sends the status of the seat belt adjustment function to the reversible emergency tensioning retractors via chassis CAN and on vehicles as of 01.03.2013 via chassis CAN 2, front SAM control unit and chassis CAN 1.

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 belt lock tongue is inserted into the respective belt buckle. Inserting the belt tab into the belt buckle is recognized 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 it to the reversible emergency tensioning retractors via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013). In order to tension the seat belt, the respective reversible emergency tensioning retractor directly actuates the integrated front reversible emergency tensioning retractor actuator motor. This tightens the belt strap at a constant speed until the seat belt slack has been reduced.

Additional function requirements for positioning the front passenger seat (with code (275) Memory package for electrically adjustable front seats)

Front passenger seat occupied
Seat adjustment normalized

Detailed information on the seat occupied recognition is available in the separate function description "Supplemental restraint system, function".

Function sequence for positioning the front passenger seat (with code (275) Memory package for electrically adjustable front seats)

In order to optimize the protective effect of the conventional restraint equipment, the front passenger seat in 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 via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (from 01.03.2013), front SAM 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 range is reached (front passenger seat in optimum position)
The impact occurs
The PRE-SAFE® situation ends

Detailed information about adjusting the front passenger seat can be found in the separate "Electrical seats, function" function description in the "Electrical seat adjustment (ESE), function" subfunction.

The PRE-SAFE® setting of the front passenger seat can be canceled at any time by making 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.

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 unit reads in the status of the respective belt buckle restraint system switch directly and sends it to the front passenger seat control unit it via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and interior CAN.

Additional function requirements for adjusting the seat contour (with code (432) Active multicontour seat)

Seat belt applied

The supplemental restraint system control unit reads in the status of the respective belt buckle restraint system switch directly and sends it via chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and interior CAN to the left front active multicontour seat control unit and to the right front active multicontour seat control unit.

Function sequence for adjusting the seat contour (with code (432) Active multicontour seat)

In order to optimize the protective effect of the conventional restraint equipment, the seat contour of the driver and front passenger seat is adjusted 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 the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit, and interior CAN to the active 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
The PRE-SAFE® situation ends

Detailed information about adjusting the seat contour can be found in the separate "Electric seats, function" function description in the "Active multicontour seat, function" subfunction.

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

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 via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM 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

The side windows are then closed until only a gap is left.

The PRE-SAFE® setting continues until:

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

Detailed information about controlling the side windows can be found in the separate function description "Power windows (EFH), function".

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.

Additional function requirements for closing of sliding roof (with code (414) Power glass tilting/sliding roof)

Sliding roof NORMALIZED

Function sequence for closing the sliding roof (with code (414) Power glass tilting/sliding roof)

The sliding roof is fully closed if it was open in the lifting direction before the PRE-SAFE® measure occurred. If the sliding roof was open in the sliding direction before the PRE-SAFE® measure occurred, it is closed apart from a residual gap. This 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 the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit, and interior CAN to the overhead control panel control unit. The sliding roof is then closed until only a gap is left.

The PRE-SAFE® setting continues until:

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

Detailed information on actuating the sliding roof is available in the separate function description titled "Power tilting/sliding roof (SHD), function".

The automatic reversing function is active when the sliding roof is being closed. If required, the closing process is reversed. Closing the sliding roof can be aborted at any time by means of manual adjustment. Following completion of the PRE-SAFE® situation, the sliding roof must be manually moved back into the desired position.

Function sequence for display of fault messages

If the reversible emergency tensioning retractors detect faults, appropriate messages 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.

On vehicles up to 28.02.2013, the reversible emergency tensioning retractors send the request for displaying a fault message to the instrument cluster via chassis CAN and on vehicles as of 01.03.2013 via chassis CAN 1, front SAM control unit and chassis CAN 2.

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. To do this, the Electronic Stability Program control unit takes the information about the PRE-SAFE® status from the chassis CAN (up to 28.02.2013) or from chassis CAN 1 (as of 01.03.2013).

The positioning of the front passenger seat and the adjustment of the seat contour of the driver or front passenger seat is aborted. Closing of the side windows or the sliding 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	MODEL 218 up to model year 2014	PE91.40-P-2051-97XAA
Electrical function schematic, pre-safe	MODEL 218 as of model year 2014	PE91.40-P-2051-97XAB
Overview of PRE-SAFE system components		GF91.40-P-9997FQ