GF91.40-P-0001FL Pre-Safe Function
GF91.40-P-0001FL PRE-SAFE Function
Function requirements, general
^ Circuit 15 On
^ Vehicle speed v > 30 km/h
^ Circuit 61 ON
The circuit 15 status is sent by the electronic ignition lock control unit (N73) to the chassis CAN (CAN E).
The status of circuit 61 is provided by the CDI control unit (N3/9) (on diesel engine) or by the motor electronics control unit (N3/10) (on gasoline engine) on the chassis CAN.
PRE-SAFE, general
The PRE-SAFE function is activated in critical driving states, 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) or Electronic Stability Program control unit Premium (N30/7) (with code (233) DISTRONIC PLUS).
The PRE-SAFE function consists of the following subfunctions:
^ Function sequence for seat belt slack reduction
^ Function sequence for sensing 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 all door windows
^ Function sequence for automatic closing of tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof) or panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Display of fault messages function sequence
^ 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 insertion of the seat belt latch into the seat belt buckle triggers the seat belt slack reduction function. This is detected by the driver seat belt buckle restraint system switch (S68/3) and front passenger seat belt buckle restraint system switch (S68/4) by the supplemental restraint system control unit (N2/10).
The left front reversible emergency tensioning retractor (A76) and right front reversible emergency tensioning retractor (A76/1) now pretension 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 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 sent over 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 the Electronic Stability Program via the vehicle dynamics CAN (CAN H).
The triggering threshold for the PRE-SAFE function is increased when the electronic stability program (ESP) is switched off manually using the ESP button (S6/1s5) in instrument panel switch group (S6/1).
The signals of the instrument panel switch group are read in over the instrument panel LIN (LIN 1) by the front SAM control unit with fuse and relay module (N10/1). The front SAM control unit sends the signals over the chassis CAN to the Electronic Stability Program control unit.
The electronic stability program control unit differentiates the following statuses:
^ PRE-SAFE longitudinal dynamics
^ PRE-SAFE lateral dynamics
PRE-SAFE longitudinal dynamics
The PRE-SAFE longitudinal dynamics are recognized by the following events:
- Emergency stop:
Driver presses down hard on the pedal (e.g. startled reaction)
- Secondary brake application as a result of a panic reaction: Vehicle does not decelerate according to the driver's intention due to special weather conditions (ice, snow or aquaplaning). The driver continues to depress the brake pedal down to the maximum pedal travel.
If a PRE-SAFE longitudinal dynamics is recognized, the following functions are activated:
- Reversible emergency belt tensioning for driver and front passenger
- Adjusting front passenger seat
PRE-SAFE lateral dynamics
The PRE-SAFE lateral dynamics are recognized by the following events:
- Excessive oversteer:
A large rear axle slip angle that can no longer be stabilized by the ESP.
- Excessive understeer:
A large, front axle slip angle pending for an extended period, which can no longer be stabilized by the ESP
- Critical steering movement:
Driver steering movement which is probably due to a startled reaction and which may lead to instability of the vehicle. Activation does not take place until after speeds of v > 140 km/h have been reached. The activation characteristics become more sensitive with increasing speeds
If a PRE-SAFE lateral dynamics is recognized, the following functions are activated:
- Reversible emergency belt tensioning for driver and front passenger
- Adjusting front passenger seat
- Closing all door windows
- Closing the tilting/sliding roof (SHD) or panoramic sliding sunroof
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. 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.
The reaction of the reversible emergency tensioning retractors varies depending on the recognized PRE-SAFE situation:
- in the event of a longitudinal dynamics situation, the belt is tensioned as quickly as possible (within approx. t = 120 ms) to a defined power level
- in the event of a lateral dynamics situation, the tensioning time is parameterizable
At the end of the tensioning request, the belt is released again. The reversible emergency tensioning retractors are activated only if the vehicle speed is v > 30 km/h and the latches of the seat belts are inserted into the seat belt buckles. This is detected via the driver seat belt buckle restraint system switch and front passenger 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 buckles over the chassis CAN to the Electronic Stability Program control unit.
If the speed drops below v = 30 km/h during a PRE-SAFE situation, all PRE-SAFE functions remain active until the speed has dropped below v = 3 km/h.
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 setting at any given time, the following adjustments can be made:
- Seat fore/aft position
- by passenger seat longitudinal adjustment seat adjustment motor (M28/1)
- Seat height
- by front passenger seat height adjustment seat adjustment motor (M28/2)
- Seat inclination
- by front passenger seat inclination adjustment seat adjustment motor (M28/3)
- Backrest inclination
- by front passenger seat backrest inclination seat adjustment motor (M28/5)
The automatic adjustment of the front passenger seat can be interrupted at any time by operating the right front seat adjustment switch group (S23).
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 to the position before the PRE-SAFE situation, but rather has to be adjusted via the right front seat adjustment switch group as necessary.
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.
The status of the front passenger seat belt buckle restraint system switch is read in by the supplement restraint system control unit and transmitted to the front SAM control unit via chassis CAN. This then transmits the status to the front passenger seat control unit over the interior CAN.
Function sequence for closing all door windows
The signal for closing the window is transmitted by the front SAM control unit via 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 windows are closed to a gap of approx. s = 50 mm with the following power window motors:
- Left front door power window motor (M10/3)
- Right front door power window motor (M10/4)
- Left rear door power window motor (M10/5)
- Right rear door power window motor (M10/6)
This ensures that the smoke particles emitted from the pyrotechnical restraint equipment can escape after any impact. The anti-pinch protection is active when the windows are closed via PRE-SAFE. If required, the closing process is reversed.
Closing the corresponding windows can be stopped any time by a manual request over the following switches:
- Driver-side power window and outside mirror adjustment switch group (S20)
- Passenger-side power window switch (S21/2)
- Left rear power window switch (S21/3)
- Right rear power window switch (S21/4)
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.
Following the PRE-SAFE situation, the windows must be manually moved back into the desired position.
Function sequence for automatic closing of tilting/sliding roof (with code (414) Power glass tilting/sliding roof) or of the panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof)
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 over the interior CAN to the overhead control panel control unit (N70) (with code (414) Power glass tilting/sliding roof) or the panoramic sliding sunroof control module (A98) (with code (413) Panoramic glass sunroof with top sliding sunroof).
The roof is closed leaving a gap of approx. s = 50 mm in order to ensure that, in the event of any subsequent impact the smoke particulates generated by the pyrotechnical restraint equipment are then extracted.
The closing procedure can be interrupted at any given time by manually operating the tilting/sliding roof switch (N70s1) (with code (414) Electric glass tilting/sliding roof) or the panoramic sliding sunroof switch (N70/3s1) (with code (413) Panoramic glass sunroof with top sliding sunroof)
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.
The roof's PRE-SAFE function can be switched off using the diagnostic tester.
Display of fault messages function sequence
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
PRE-SAFE is deactivated as soon as a PRE-SAFE longitudinal dynamics situation or PRE-SAFE lateral dynamics situation is no longer present.
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 over the 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 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 restraint systems control unit, all adjustments are stopped immediately.
