PRE-SAFE function - GF91.40-P-0001SX
MODEL 221.0 /1, 216.3 up to Model Year 8
Description
The PRE-SAFE safety system includes a package with the following functions:
- Reversible electromotive belt tensioning for driver and front passenger (with model 221)
- Positioning of the front passenger by adjusting the front passenger seat
- Automatic closing of all door windows
- Rear occupant positioning by adjusting the individual rear seats (with model 221 with code (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints)
- Automatic closing of tilting/sliding roof (SHD) (with model 221 with code (414) Power glass tilting/sliding sunroof or model 216)
- Adjust the seat contour of the driver seat and front passenger seat (with code (409) Left/right front multicontour seat or code (432) Left and right dynamic multicontour seat)
- Adjust the seat contour of the left and right rear seats (with model 221 with code (406) Rear multicontour seat)
PRE-SAFE is activated in the event of critical drive situations, i.e. 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.
Function requirements
- Circuit 15 On
- Vehicle speed v > 30 km/h (forward travel)
PRE-SAFE activation
The data of the ESP control unit (N47-5), the yaw rate, lateral and longitudinal acceleration sensor (B24/15) and the DTR controller unit (A89) (with code (233) Distronic Plus) are evaluated for activating PRE-SAFE functions.
PRE-SAFE is activated in the event of the following critical drive situations:
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
- Partial braking by PRE-SAFE brake (with code (233) Distronic Plus):
Imminent impact detected
PRE-SAFE lateral dynamics
- Severe oversteer:
A large rear axle slip angle that is beyond manageable driving physics and cannot be stabilized by the Electronic Stability Program (ESP)
- Severe understeer:
A large front axle slip angle that is present for an extended period of time and is beyond the manageable driving physics and cannot 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 sensible with increasing speeds
The following table illustrates which functions are activated with PRE-SAFE longitudinal dynamics or PRE-SAFE lateral dynamics.
| Activated PRE-SAFE function | PRE-SAFE longitudinal dynamics | PRE-SAFE lateral dynamics |
|---|---|---|
| Reversible emergency tensioning retraction | X | X |
| Positioning of front passenger seat | X | X |
| Closing of side windows | - | X |
| Positioning of rear seats | X | X |
| Closing of tilting/sliding roof | - | X |
| Adjust seat contour | X | X |
The sequence of PRE-SAFE activities is coordinated by the ESP control unit, which is connected to the interior CAN via the chassis CAN and the central gateway control unit (N93). The existing vehicle systems are used to realize the PRE-SAFE function.
Reversible belt tensioning, function (with model 221)
The left front reversible emergency tensioning retractor (A76) and the right front reversible emergency tensioning retractor (A76/1) reduce the existing seat belt slack in dangerous situations. This secures the occupants in the seats at an early stage.
In the event of an accident, the occupants are thus restrained in a favorable position in which the restraint equipment can achieve an ideal protective effect.
The reversible emergency tensioning retractors receive the signal for emergency tensioning retraction via the chassis CAN from the ESP control unit.
At the end of the tensioning request, the belt is released again.
The reaction of the reversible emergency tensioning retractors varies depending on the recognized PRE-SAFE situation:
- In a longitudinal dynamics situation, the belt strap is tensioned as fast as possible (within approx. 120 ms) to a defined force level
- in a lateral dynamics situation, the tensioning time is parameterizable
The reversible emergency tensioning retractors are only activated when the vehicle speed is v > 30 km/h and the seat belts are fastened. If the seat belts have been fastened, this is detected via the driver seat belt buckle and seat belt reminder warning switch (S68/1) and the front passenger seat belt buckle and seat belt reminder warning switch (S68/2), read in by the restraint systems control unit (N2/7) and sent via the chassis CAN to the reversible emergency tensioning retractors.
If during a PRE-SAFE situation the speed
drops below v = 30 km/h, all PRE-SAFE functions remain active until the speed drops below v = 3 km/h.
Front passenger seat adjustment
Additional function requirements
- Normalized front passenger seat
- Front passenger seat moved to an unfavorable position (e.g. reclining position)
- Front passenger seat recognized as occupied (up to 31.05.07)
As of 1.6.07 the positioning of the front passenger seat is also active even when the front passenger seat is not occupied.
Function
Adjustment of the front passenger seat is used to move the front passenger into a favorable position in the event of an imminent impact. In this position, the conventional restraint systems can provide the best protective effect possible.
The adjustment of the front passenger seat is coordinated by the right front seat control unit (N32/2). The automatic adjustment of the front passenger seat can be interrupted at any time by operating the right front seat operation 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)
- The impact starts
- 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 seat operation switch group, if necessary.
Seat adjustment takes place depending on the front passenger seat belt status. The status of the front passenger seat belt buckle and seat belt reminder warning switch is transmitted to the central gateway control unit by the restraint systems control unit via the chassis CAN, from where it is relayed to the right front seat control unit via the interior CAN.
Seat adjustment if the occupants are not buckled up
Depending on how the front passenger seat is positioned the following settings are optimized:
- Backrest angle
- Seat cushion inclination
- Seat height
- Fore/aft adjustment of complete front passenger seat
Seat adjustment if the 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 PRE-SAFE function of the front passenger seat can be switched off via STAR DIAGNOSIS.
Determination of front passenger seat occupation (up to 31.5.07 function relevant)
Vehicles without code (494) USA version
- The restraint systems control unit evaluates the front passenger seat occupied and child seat recognition sensor (B48) and sends the occupation status via the interior CAN.
Model 221 with code (494) USA version:
- The WSS control unit (Weight Sensing System) (N2/13) evaluates the WSS (Weight Sensing System) sensors (B48/11, B48/12, B48/13, B48/14) and sends the occupation status via the interior CAN.
Model 216 with code (494) USA version:
- The Weight Sensing System (WSS) control unit (N110) evaluates the belt tension sensor (B48/3) and the seat occupied recognition pressure sensor (B48/4) and sends the occupation status via the interior CAN.
Rear seat adjustment
Additional function requirements
- Rear seats normalized
- Rear seats set to an unfavorable position
Function
Rear seat adjustment is used to move the rear occupants into a favorable position in the event of an imminent impact. In this position, the restraint equipment can provide the best protective effect possible. Seat adjustment takes place depending upon whether the rear occupants are buckled up or not.
The status of the left rear seat belt buckle switch (S68/11) and the right rear seat belt buckle switch (S68/12) is forwarded by the rear SAM control unit with fuse and relay module (N10/2) via the interior CAN to the central gateway control unit, and from there via the interior CAN to the rear seats control unit (N25/6).
Seat adjustment if the occupants are not buckled up
Dependent upon how the rear seats are set, the:
- inclination of the head restraint is adjusted
- backrest is adjusted
- seat cushion inclination is adjusted
Seat adjustment if the 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 adjustment process lasts until:
- The target area is reached (seat in ideal position)
- The impact starts
- The PRE-SAFE situation ends
The PRE-SAFE function of the rear seats can be switched off via STAR DIAGNOSIS.
Close tilting/sliding roof
Additional function requirements
- Normalized tilting/sliding roof
Function
Closing the tilting/sliding roof via 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) receives the signal from the central gateway control unit via the interior CAN and closes the tilting/sliding roof via the roof system drive unit (M12).
The tilting/sliding roof is closed leaving a gap of approx. 50 mm in order to ensure that, in the event of a possible, subsequent impact, smoke particles generated by the pyrotechnical restraint systems can escape. Closing can be aborted at any time by manually operating the roof switch (N70s1).
The anti-pinch protection is active when the tilting/sliding 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 tilting/sliding roof must be manually moved back into the desired position.
The PRE-SAFE function of the tilting/sliding roof can be switched off via STAR DIAGNOSIS.
Window closing
Additional function requirements
- Power window normalized
Function
Closing the windows via 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 following control units receive the signal via the interior CAN from the central gateway control unit and authorize closure of the windows:
Model 221:
- 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)
Model 216:
- Left door control unit (N69/1)
- Right door control unit (N69/2)
The windows are closed leaving a gap of approx. 50 mm in order to ensure that, in the event of the possible subsequent impact, smoke particles generated by the pyrotechnical restraint systems can escape.
The anti-pinch protection is active when the windows are closed via PRE-SAFE. If required, the closing process is reversed. Closing can be aborted at any time by means of a manual request.
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.
Adjustment of seat contour
Additional function requirements
- Corresponding seat occupied (seat belt fastened)
Function
The purpose of inflating the side inserts in the seats is to centrally secure the occupants in position in the seats. In this position, the restraint equipment can provide the best protective effect possible.
The following control units receive the signal to adjust the seat contour via the interior CAN from the central gateway control unit:
With code (409) Left/right front multicontour seats:
- Left front multicontour backrest control unit (N32/15)
- Right front multicontour backrest control unit (N32/16)
With code (432) Left and right dynamic multicontour seat:
- Left front dynamic seat control unit (N32/19)
- Right front dynamic seat control unit (N32/22)
Model 221 with code (406) Rear multicontour seat:
- Left rear multicontour backrest control unit (N32/20)
- Right rear multicontour backrest control unit (N32/21)
The seat contour is adjusted until the PRE-SAFE specified pressure is reached or until the end of the PRE-SAFE situation. After the PRE-SAFE situation has ended, the filling status of the side inserts is returned to the particular initial status it had before PRE-SAFE was activated.
The adjustment of the seat contour can be aborted at any time via a manual adjustment or a memory request.
PRE-SAFE brake, function
The data of the DTR controller unit are used by the radar sensors control unit (SGR) (N62/1) to continuously calculate the hazard potential for a rear-end collision. If a critical situation is recognized, the system starts by issuing an optical warning in the instrument cluster (A1) in the form of a red triangle. In addition, a warning tone is sounded.
If the driver does not react accordingly, the PRE-SAFE system independently applies partial braking.
This helps to ask the driver to take action; at the same time, the situation is relieved somewhat through the brake application and, in the event of an impact, the impact energy is reduced. The reversible emergency tensioning retractor are deployed at the same time.
The ESP control unit carries out the PRE-SAFE brake application with the aid of the signals from the radar sensors control unit via vehicle dynamics CAN.
The PRE-SAFE brake is deactivated when:
- an object is no longer recognized
- the speed is < 3 km/h
- the driver reduces the brake pressure
- the driver accelerates
- the steering movement indicates a deactivation intention
Function when the ESP is switched off
The activation threshold for the PRE-SAFE functions is increased, if the ESP has been shut off manually via the ESP OFF switch (S6/2s11) in the cockpit switch group (S6/2).
Error messages
If a fault is detected in the reversible emergency tensioning retractors, this is indicated 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.
Ending the PRE-SAFE functions
PRE-SAFE is deactivated as soon as a PRE-SAFE longitudinal dynamics situation or lateral dynamics situation is no longer present. The ESP control unit transmits a signal for shutting off the PRE-SAFE functions via the chassis CAN. The signal is transmitted to the involved control units via the central gateway control unit over the interior CAN.
The following adjustments are aborted by the corresponding control units, if the PRE-SAFE position has not yet been reached:
- Adjustment of the front passenger seat and rear seats
- Adjustment of the seat contour
Closing of the windows and the tilting/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.
In the event of an impact that is detected by the restraint systems control unit, all adjustments are stopped immediately.
| PRE-SAFE, location of components | Model 221 | GF91.40-P-0001-01SX | |
| Model 216 | GF91.40-P-0001-01SC | ||
| PRE-SAFE, networking of components | Model 221 | GF91.40-P-0001-02SX | |
| Model 216 | GF91.40-P-0001-02SC | ||
| PRE-SAFE, block diagram | Model 221 | GF91.40-P-0001-03SX | |
| Model 216 | GF91.40-P-0001-03SC | ||
| Instrument cluster, component description | A1 | GF54.30-P-6000SX | |
| Front reversible emergency tensioning retractor, component description | A76, A76/1 Model 221 |
GF91.40-P-4020SX | |
| DTR controller unit, component description | A89 Model 216 with engine 273, 275 and code (233) Distronic Plus Model 221 with engine 272, 273, 275, 642, 629 and code (233) Distronic Plus |
GF30.30-P-3210SX | |
| Yaw rate and lateral acceleration sensor, component description | B24/15 | GF42.45-P-5120SX | |
| Seat occupied recognition with automatic child seat recognition, component description | B48 Vehicles up to 31.5.07 without code (494) USA version Vehicles as of 1.6.07 with code (U18) Automatic child seat recognition (ACSR [AKSE]) |
GF91.60-P-4035SX | |
| Belt tension sensor component description | B48/3 Vehicles with code (494) USA version |
GF91.60-P-4108SXU | |
| Front passenger seat pressure sensor, component description | B48/4 Model 216 with code (494) USA version |
GF91.60-P-4060SCU | |
| WSS (Weight Sensing System) sensor, component description | B48/11, B48/12, B48/13, B48/14 Model 221 with code (494) USA version |
GF91.60-P-4036SXU | |
| Restraint systems control unit, component description | N2/7 | GF91.60-P-4048SX | |
| WSS (Weight Sensing System) control unit, component description | N2/13 Model 221 with code (494) USA version |
GF91.60-P-4046SXU | |
| N110 Model 216 with code (494) USA version |
GF91.60-P-4046SCU | ||
| Rear SAM control unit with fuse and relay module, component description | N10/2 | GF54.21-P-6030SX | |
| Rear seats control unit, component description | N25/6 Model 221 with code (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints |
GF91.29-P-5250SXA | |
| Right front seat control unit, component description | N32/2 | GF91.29-P-5240SX | |
| Multicontour seat control unit (MCS), component description | N32/15, N32/16 with code (409) Left/right front multicontour seats |
GF91.25-P-5201SX | |
| N32/20, N32/21 Model 221 with code (406) Rear multicontour seat |
GF91.25-P-5201SXA | ||
| Dynamic seat control unit, component description | N32/19, N32/22 Vehicles with code (432) Left and right dynamic multicontour seat |
GF91.25-P-5202SX | |
| ESP control unit, component description | N47-5 | GF42.45-P-5118SX | |
| Component description for radar sensors control unit | N62/1 Model 216 with engine 273, 275 and code (233) Distronic Plus Model 221 with engine 272, 273, 275, 642, 629 and code (233) Distronic Plus |
GF30.30-P-3301SX | |
| Driver-side front door control unit, component description | N69/1 Model 221 |
GF72.29-P-6000SX | |
| Model 216 | GF72.29-P-6000SC | ||
| Passenger-side front door control unit, component description | N69/2 Model 221 |
GF72.29-P-6010SX | |
| Model 216 | GF72.29-P-6010SC | ||
| Rear door control unit, component description | N69/3, N69/4 Model 221 |
GF72.29-P-6020SX | |
| Overhead control panel control unit, component description | N70 | GF82.20-P-5216SX | |
| Central gateway control unit, component description | N93 | GF54.21-P-4170SX | |
| ESP Off switch, component description | S6/2s11 | GF42.45-P-5121SX | |
| Driver power window, outside mirror and trunk lid switch group, component description | S20/1 | GF54.25-P-4230SX | |
| Front passenger power window switch, component description | S21/2 | GF72.29-P-6042SX | |
| Component description for rear power window switch | S21/3, S21/4 Model 221 without code (297) Roller sun blinds in rear doors, without code (413) Panoramic sliding roof and without code (540) Electric rear window roller blind, Model 216 |
GF72.29-P-6050SX | |
| Rear door power window/roller blind switch group, component description | S21/21, S21/22 Model 221 with code (297) Roller sun blinds in rear doors, with code (413) Panoramic sliding roof or with code (540) Electric rear window roller blind |
GF72.29-P-6041SX | |
| Front seat adjustment switch group, component description | S23 | GF91.29-P-5220SX | |
| Seat belt buckle switch component description | S68/1, S68; S68/11, S68/12 (with model 221 with code (223) Rear seat bench with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints) |
GF91.60-P-4045SX |