GF91.40-P-0001CE Pre-Safe Function
GF91.40-P-0001CE PRE-SAFE Function
- with CODE (299) PRE-SAFE
Function requirements, general
^ Circuit 15 ON
^ Vehicle speed v > 30 km/h (not for seat belt slack reduction)
^ Circuit 61 On (not for seat belt slack reduction)
The status of circuit 15 is provided by the electronic ignition lock control unit (N73) via chassis CAN (CAN E).
PRE-SAFE, general
The PRE-SAFE system 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 Electronic Stability Program control unit (N30/4) data are evaluated for triggering the PRE-SAFE functions.
The PRE-SAFE system consists of the following subfunctions:
^ Function sequence for seat belt slack reduction (as of 1.6.09)
^ Function sequence for possible activation criteria
^ Function sequence when Electronic Stability Program (ESP) is disabled
^ Function sequence for reversible emergency tensioning retractors for driver and front passenger
^ Function sequence for adjustment of front passenger seat (with code (242) Electrically adjustable front passenger seat with memory)
^ Function sequence for closing all door windows
^ Function sequence for automatic closing of tilting/sliding roof (SHD) (with code (414) Electric glass tilting/sliding roof) or automatic closing of panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Function sequence for display of fault messages
^ Function sequence for ending the PRE-SAFE functions
Additional function requirements for seat belt slack reduction (as of 1.6.09)
^ Function in instrument cluster (A1) activated
^ PRE-SAFE has not been activated
Function sequence for seat belt slack reduction (as of 1.6.09)
The seat belt slack reduction function reduces the existing seat belt slack once the seat belt is fastened.
The insertion of the seat belt tab into the 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 possible activation criteria
The possible activation criteria are made up of the following partial functions:
^ Function sequence for PRE-SAFE longitudinal dynamics
^ Function sequence for PRE-SAFE lateral dynamics
Function sequence for PRE-SAFE longitudinal dynamics
- 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.
Function sequence for PRE-SAFE lateral dynamics
- 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 speeds of v > 140 km/h have been reached. The activation characteristics become more sensitive with increasing speeds
Function sequence when the ESP is switched off
The triggering threshold for the PRE-SAFE functions is increased when the ESP is switched off manually using the ESP button (S6/1s5) (model 204.9, model 204.0/2 up to 31.5.10) 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.
With model 204.0/2, the previous functionalities of the ESP button can be selected via a menu in the instrument cluster as of 1.6.10.
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 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 adjustment of front passenger seat (with code (242) Electrically adjustable front passenger seat with memory)
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 the seat fore/aft adjustment seat adjustment motor, front passenger seat (M28/1)
- Seat height by height adjustment seat adjustment motor, front passenger seat (M28/2)
- Seat inclination by inclination adjustment seat adjustment motor, front passenger seat (M28/3)
- Backrest inclination by backrest inclination seat adjustment motor, front passenger seat (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 time takes until:
- The target area has been reached (seat in optimum position)
- The 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 sent by the supplemental restraint system control unit over the chassis CAN to the front SAM control unit and forwarded there over the interior CAN (CAN B) to the front passenger seat control unit.
Function sequence for closing all door windows
In the event of a PRE-SAFE situation, the front SAM control unit sends the signal to close the windows 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 windows are closed by the left front door power window motor (M10/3), right front door power window motor (M10/4), left rear door power window motor (M10/5) and the right rear door power window motor (M10/6) to a gap of approx. s = 50 mm, to ensure that in the event of any subsequent impact the smoke particulates generated by the pyrotechnical restraint equipment are then extracted.
The anti-pinch protection is active when the windows are closed via PRE-SAFE. If required, the closing process is reversed.
Closing by PRE-SAFE can be interrupted at any given time through a manual request from the:
- Driver side power window switch group and outside mirror adjustment (S20) or the
- Passenger side power window switch, (S21/2) or the
- Left rear power window switch (S21/3) or the
- Right rear power window switch (S21/4) for each window.
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 (SHD) (with code (414) Electric glass tilting/sliding roof) or automatic closing of panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof)
Closing the roof using PRE-SAFE is intended to prevent objects from penetrating the vehicle interior and stop the occupants' body parts (such as arms) from protruding out of the vehicle if an accident occurs.
The overhead control panel control unit (N70) (with code (414) Electric glass tilting/sliding roof) or panoramic sliding sunroof control unit (A98) (with code (413) Panoramic glass sunroof with top sliding sunroof) receives the request from the Electronic Stability Program control unit over the interior CAN from the front SAM control unit and then authorizes the roof to be closed. To do so, the tilting/sliding roof drive unit (M12) is actuated accordingly by the overhead control panel control unit or the panoramic sliding sunroof roller sun blind drive unit (M12/5) by the panoramic sliding sunroof control module.
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 PRE-SAFE function of the roof can be switched off using the diagnostic tester.
Function sequence for display of fault messages
If a fault is recognized with reversible emergency tensioning retractors, this is shown in the travel distance display (A1p7) (model 204.0/2/9 (except 204.077/277) without code (442) Comfort multifunction steering wheel) or in the multifunction display (A1p13) (with code (442) Comfort multifunction steering wheel, model 204.077/277) of the instrument cluster. Faults of other components that are part of PRE-SAFE are not displayed as PRE-SAFE faults.
Function sequence for ending the 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 via interior CAN to the involved control units.
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.
If the supplemental restraint system control unit detects an impact, then all adjustments are immediately stopped.
