GF91.40-P-0001FQ Pre-Safe Function

GF91.40-P-0001FQ PRE-SAFE Function
MODEL 218

Function requirements, general
^ Circuit 15 ON
^ "PT_Rdy" signal set

The electronic ignition lock control unit (N73) provides the status of circuit 15 over the chassis CAN (CAN E).
The"PT_Rdy" signal is sent by the CDI control unit (N3/9) (with diesel engine) or by the ME-SFI [ME] control unit (N3/10) (with gasoline engine) over the chassis CAN.

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 during the expected accident by activating the functions before the actual impact.
The PRE-SAFE function is controlled by the Electronic Stability Program control unit (N30/4) (without code (233) DISTRONIC PLUS except 218.374) or Premium Electronic Stability Program control unit (N30/7) (with code (233) DISTRONIC PLUS or model 218.374).

The PRE-SAFE function consists of the following subfunctions:
^ Function sequence for seat belt slack reduction
^ Function sequence for sensing the vehicle status
^ Function sequence for reversible emergency tensioning retractors for driver and front passenger
^ Function sequence for adjusting front passenger seat (with code (275) Memory package for electrically adjustable front seats)
^ Function sequence for closing the side windows
^ Function sequence for automatic closing of tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof)
^ Function sequence for adjusting seat contour (with code (432) Active multicontour seat)
^ Function sequence for display of fault messages
^ Function sequence for terminating PRE-SAFE functions

Additional function requirements for seat belt slack reduction
^ Function in instrument cluster (A1) activated
^ PRE-SAFE has not been activated

Function sequence for seat belt slack reduction
The seat belt slack reduction function reduces the existing seat belt slack once the seat belt is fastened.
The function is actuated by inserting the seat belt latch into the seat belt buckle. The insertion is detected by way of the driver seat belt buckle restraint system switch (S68/3) and the front passenger seat belt buckle restraint system switch (S68/4) from the Supplemental Restraint System control unit (N2/10). The Supplemental Restraint System control unit sends the status of the seat belt buckle restraint system switch over the chassis CAN to the left front reversible emergency tensioning retractor (A76) and the right front reversible emergency tensioning retractor (A76/1).
The reversible emergency tensioning retractors then tighten the belt strap at a speed of v = 50 mm/s (± 10 %) until the seat belt slack is reduced. The belt force generated here increases at the end of the pretensioning process to F = 20 N (±20 %). Once the belt force has been reached, the seat belt is pretensioned for another t = 400 ms.
Following expiration of this time, the seat belt slack reduction function is ended.

Function sequence for sensing the vehicle status
The vehicle status is sensed by the electronic stability program control unit. For this purpose information is evaluated by the following components in addition to the internal data:
- Steering angle sensor (N49)
- Yaw rate sensor for lateral and longitudinal acceleration (B24/15)

The signals from the steering angle sensor are read in by the steering column tube module control unit (N80) and made available via the chassis CAN to the Electronic Stability Program control unit.
The signals from the yaw rate sensor for lateral and longitudinal acceleration are read in by electronic stability program control unit via the vehicle dynamics CAN.

The signals of the following control units are also read in over chassis CAN:
- DISTRONIC electric controller unit (A89) (with code (233) DISTRONIC PLUS)
- Video and radar sensor system control unit (N62/2) (with code (237) Active Blind Spot Assist)

The triggering threshold for the PRE-SAFE functions is increased when the Electronic Stability Program (ESP) was manually switched to passive in a menu in the instrument cluster.

The electronic stability program control unit differentiates the following 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 oversteer:
Swerving of vehicle rear connected with severe ESP stabilization interventions
- Strong understeer:
Vehicle pushes for a longer time over the front wheels
- Critical steering motion:
Fast steering motion at high speeds (v > 140 km/h), which indicate a startled response by the driver and which will most likely result in driving conditions that are beyond the capability of a normal driver
- Strong braking support through the Brake Assist System (BAS) (with code (233) DISTRONIC PLUS):
Strong support of driver braking action in response to recognized threat of collision in longitudinal traffic based on a radar supported assessment of the surroundings
- Autonomous partial braking through PRE-SAFE brake (with code (233) DISTRONIC PLUS):
Pronounced partial deceleration output of vehicle at recognized risk of collision in longitudinal traffic through PRE-SAFE brake based on a radar-supported assessment of the surroundings
- Autonomous emergency braking though PRE-SAFE brake (with code (233) DISTRONIC PLUS):
Emergency braking request through PRE-SAFE brake in event of inevitable risk of collision in longitudinal traffic based on a radar- supported assessment of the surroundings
- Collision object recognition at front (with code (233) DISTRONIC PLUS):
Recognition of an immediately imminent frontal impact (under certain conditions) by means of short-range radar sensor system independent of assistance system interventions (e.g. cornering, oncoming traffic)
- Autonomous course correction through active Blind Spot Assist (with code (237) Active Blind Spot Assist):
Pronounced, course-correcting intervention for registered risk of a side collision with vehicles in blind spot based on a radar- supported assessment of surroundings

The following measures can be initiated in the event of a recognized hazard situation to improve occupant protection:
- Reversible emergency tensioning retraction
- Adjustment of front passenger seat (with code (275) Memory package for electrically adjustable front seats)
- Close side windows
- Function sequence for automatic closing of tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof)
- Adjustment of seat contour (with code (432) Active multicontour seat)

Function sequence for reversible emergency tensioning retractors for driver and front passenger
The left front reversible emergency tensioning retractor and the right front reversible emergency tensioning retractor reduce the existing seat belt slack in dangerous situations. Thus, the occupants are secured in position in the seats at an early point in time in order to prevent displacement.
The occupants are therefore held in a favorable seat position in the event of an accident, allowing the conventional restraint systems to have their optimum protective effect. In the event of a rollover the reversible emergency tensioning retractors are also triggered.
The reversible emergency tensioning retractors receive the signal for emergency tensioning retraction via the chassis CAN from the Electronic Stability Program control unit. The left front reversible emergency tensioning retractor actuator motor (M68) and right front reversible emergency tensioning retractor actuator motor (M68/1) integrated in the respective reversible emergency tensioning retractor are directly actuated for pretensioning.
Depending on the situation the belt is tightened with varying force or speed.
At the end of the tensioning request, the belt is released again.
Following a rollover the belt strap is no longer released.
The reversible emergency tensioning retractors are only activated when the seat belt latches are inserted into the seat belt buckles.
This is detected through the seat belt buckle restraint system switch by the Supplemental Restraint System control unit.
The Supplemental Restraint System control unit sends the status of the seat belt buckle restraint system switch over chassis CAN to the reversible emergency tensioning retractors.

Function sequence for adjusting front passenger seat (with code (275) Memory package for electrically adjustable front seats)
Adjustment of the front passenger seat is controlled by the front passenger seat control unit (N32/2).
Depending on the seat adjustment at any given time, the following adjustments can be made:
- Seat fore/aft position
- Seat height
- Seat inclination
- Backrest inclination

The automatic adjustment of the front passenger seat can be interrupted at any given time by a manual adjust request.
If a PRE-SAFE situation continues to be present, the front passenger seat is adjusted again via PRE-SAFE after the manual adjustment has been completed.

The adjustment process lasts until:
- The target area is reached (front passenger seat in ideal position)
- An impact occurs
- - The PRE-SAFE situation ends

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 occupants are not buckled up
The system moves the seat into a position that is suitable for situations that are unfavorable with regard to safety technology.
Detailed information on seat adjustment control is available in the separate function description for electrical seat adjustment (ESE).
The status of the front passenger seat belt buckle restraint system switch is read in by the supplement restraint system control unit and sent to the front SAM control unit over the chassis CAN. It transmits the status to the front passenger seat control unit via the interior CAN (CAN B).

Function sequence for closing the side windows
The signal for closing the side windows is sent by the front SAM control unit over the interior CAN to the following control units:
- Left front door control unit (N69/1)
- Right front door control unit (N69/2)
- Left rear door control unit (N69/3)
- Right rear door control unit (N69/4)
The side windows are closed until only a gap is left. This serves to ensure that in the event of the possible subsequent impact, smoke particles that are produced as a result of the pyrotechnical restraint equipment can be exhausted.

The anti-pinch protection is active when the side window is closed through PRE-SAFE. If required, the closing process is reversed.
The closing of each side window can be interrupted by a manual adjustment request at any given time.
If closing is activated via PRE-SAFE during an automatic lowering process, the automatic lowering process is aborted and closing is carried out via PRE-SAFE.
The side windows have to be manually moved back into the desired position after the PRE-SAFE situation has ended.
Detailed information on controlling the side windows is available in the separate function description for the power windows (EFH).

Function sequence for automatic closing of tilting/sliding roof (with code (414) Power glass tilting/sliding roof)
Closing the roof via PRE-SAFE is intended to prevent objects from penetrating the vehicle interior and stop occupant body parts (such as arms) from protruding from the vehicle if an accident occurs.
The Electronic Stability Program control unit transmits the request to close the roof to the front SAM control unit via the chassis CAN.
This sends the request to the overhead control panel control unit (N70) over the interior CAN.
The roof is closed leaving a gap in order to ensure that, in the event of the possible subsequent impact, smoke particles that are produced as a result of the pyrotechnical restraint equipment can be exhausted.
Closing can be aborted at any time by means of a manual adjustment request.
The anti-pinch protection is active when the roof is being closed. If required, the closing process is reversed.
If closing is activated via PRE-SAFE during a manual adjustment, the manual adjustment request is completed first and then closing via PRE-SAFE.
If closing is activated via PRE-SAFE during an automatic process, the automatic process is aborted and closing is carried out via PRE-SAFE.
Following the PRE-SAFE situation, the roof must be manually moved back into the desired position.
Detailed information on actuating the roof is available in the separate function description for the power tilting/sliding roof (SHD).

Function sequence for adjusting seat contour (with code (432) Active multicontour seat)
The inflating of the side inserts in the seats should enable vehicle occupants to be located centrally in the seats. The lumbar support is deflated so that the occupants are seated lower down in the seat. In this position, the restraint equipment can provide the best possible protective effect.
The Electronic Stability Program control unit sends the request to adjust the seat contour to the front SAM control unit over the chassis CAN. This sends the request over the interior CAN to the left front active multicontour seat control unit (N32/19) and the right front active multicontour seat control unit (N32/22).
Detailed information on adjusting the seat contour is available in the separate function description for the active multicontour seat.

Function sequence for display of fault messages
If a fault is detected in the reversible emergency tensioning retractors, this is shown on the multifunction display (A1p13) in the instrument cluster. Faults in other components that are involved in PRE-SAFE are not displayed as PRE-SAFE faults.

Function sequence for terminating PRE-SAFE functions
The PRE-SAFE function is deactivated as soon as the situation is deemed to be no longer critical.
The Electronic Stability Program control unit sends a signal for shutting off the PRE-SAFE functions over the chassis CAN.
The front SAM control unit sends the signal via interior CAN to the involved control units.
The adjustment of the front passenger seat is canceled insofar as the PRE-SAFE position has not been reached.
Closing of the side windows and the roof is not stopped. 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.
In the event of an impact that is detected by the Supplemental Restraint System control unit, all adjustments are immediately stopped.