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

GF91.40-P-0001GM PRE-SAFE Function

Function requirements, general
^ Circuit 15 On
^ Vehicle speed v > 30 km/h

The circuit 15 status is sent by the EIS [EZS] control unit (N73) to the interior CAN (CAN B) and to the engine compartment CAN (CAN C).

The vehicle speed is transmitted by the instrument cluster (A1) to the interior CAN and to the engine compartment CAN.

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.

General information about the PRE-SAFE system
The PRE-SAFE system is activated in critical driving states, e.g. 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.

Alongside other input factors, it is mainly the data of the ESP control unit (N47-5) that are analyzed for triggering the PRE-SAFE system. The PRE-SAFE system is controlled by the left front reversible emergency tensioning retractor (A76) and the right front reversible emergency tensioning retractor (A76/1)

The PRE-SAFE system consists of the following subfunctions:
^ Function sequence for belt slack reduction (as of 1.7.09)
^ Function sequence for registering of activation criteria
^ Function sequence for Electronic Stability Program (ESP) switched to passive
^ Function sequence for reversible tensioning retraction
^ 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) Power glass tilting/sliding sunroof) or automatic closing of panoramic sliding sunroof (for model 251 with code (413) Panoramic sliding sunroof with top sliding sunroof)
^ Display of fault messages function sequence
^ Function sequence for ending PRE-SAFE

Additional function requirements for belt slack reduction (as of 1.7.09)
^ Function activated in instrument cluster
^ PRE-SAFE has not been triggered

Function sequence for belt slack reduction (as of 1.7.09)
The belt slack reduction function reduces any seat belt slack after the seat belt has been fastened.

The function is triggered when the belt latch of the seat belt is inserted into the belt buckle. This is recognized by the restraint systems control unit (N2/7) 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). The left front reversible emergency tensioning retractor and the right front reversible emergency tensioning retractor then tighten the belt strap at a rate of v = 50 mm/s (±10%) until the seat belt slack is reduced. The resulting belt force increases at the end of the tightening process to F = 20 N (±20%). When this belt force is reached, the seat belt is held taut for another t = 400 ms. At the end of this time the belt slack reduction function is terminated.

Function sequence for registering of activation criteria
The recording of the activation criteria comprises the following subfunctions:
^ Function sequence for recording vehicle longitudinal dynamics
^ Function sequence for recording the vehicle lateral dynamics

Function sequence for recording vehicle longitudinal dynamics
The speed at which the brake pedal is depressed is detected by the ESP control unit. It is thus possible to detect if the driver presses the brake pedal very quickly (e.g. startled reaction). The information "Brake Assist System (BAS) active" is made available to the reversible emergency tensioning retractors by the ESP control unit via the engine compartment CAN.

Function sequence for recording the vehicle lateral dynamics
- Excessive oversteer:
- A large rear axle slip angle that can no longer be stabilized even with the Electronic Stability Program

- 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:
- Steering movement of the driver, which is probably due to a startle reaction and can 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

The understeer/oversteer information is made available to the reversible emergency tensioning retractors by the ESP control unit via the engine compartment CAN.

The steering movement information is made available by the steering column tube module via the engine compartment CAN.

Function sequence for Electronic Stability Program switched to passive
The triggering threshold for the PRE-SAFE functions is raised if the ESP is manually switched to passive through the ESP OFF switch (N72/1s1) in the upper control panel control unit (N72/1). The upper control panel control unit transmits the signal over the interior CAN to the central gateway control unit (N93).

The central gateway control unit sends the signal via the engine compartment CAN to the ESP control unit.

Additional function requirements for reversible tensioning retraction
^ Each seat belt inserted into seat belt buckle
^ Front passenger seat recognized as occupied (during front passenger tensioning retraction)

Information regarding an inserted belt buckle is recognized by the restraint systems control unit (N2/7) via the driver seat belt buckle and seat belt reminder warning switch and the front passenger seat belt buckle and seat belt reminder warning switch and signaled to the reversible emergency tensioning retractors via the engine compartment CAN.

Information regarding an occupied front passenger seat is sent by the WSS (Weight Sensing System) control unit (N2/13) (with code (494) USA version) via the interior CAN or by the restraint systems control unit via the engine compartment CAN to the central gateway control unit.

Function sequence for reversible tensioning retraction
The reversible emergency tensioning retractors reduce any seat belt slack in hazardous situations. This secures the occupants in the seats at an early stage. The occupants are therefore held in a favorable seat position in the event of an accident, allowing the conventional restraint equipment to have their optimum protective effect.

The reversible emergency tensioning retractors receive the corresponding signals to record the driving dynamics situation from the ESP control unit via the engine compartment CAN. Depending on the situation, the belt strap is tensioned to a defined force level within the parameterizable tensioning period (up to t = 120 m

The reaction of the reversible emergency tensioning retractors varies depending on the recognized PRE-SAFE situation:
- Longitudinal dynamics situation (fastest possible tensioning of belt)
- Lateral dynamics situation (more time is available here for tensioning the belt)

At the end of the tensioning request, the belt is released again.

The belt tensioning for the front passenger is only triggered, when the front passenger seat is occupied and the respective seat belt inserted into the seat belt buckle.

Additional function requirements for adjustment of front passenger seat (with code (242) Electrically adjustable front passenger seat with memory)
^ Front passenger seat occupied recognized

Function sequence for adjustment of front passenger seat (with code (242) Electrically adjustable front passenger seat with memory)
The adjustment of the front passenger seat consists of the following subfunctions:
^ Adjustment of front passenger seat with occupant strapped in
^ Adjustment of front passenger seat with occupant not strapped in

Adjustment of front passenger seat with occupant strapped in
The adjuster for the front passenger seat is actuated by the passenger-side front seat adjustment control unit with memory (N32/2).
Depending on the setting at any given time, the following adjustments can be made:
- Seat fore/aft position, by the front passenger seat fore/aft adjustment motor (M28/1).
If the seat is positioned too far forward, it is moved back (approx. s = 100 mm away from the front stop) If the seat is positioned too far back, it is moved forward (approx. s = 50 mm away from the rear stop)

- Seat height, by the front passenger rear seat height adjustment motor (M28/2).
The seat is adjusted to the lower stop.

- Seat inclination, by the front passenger front seat height adjustment motor (M28/3).
The adjustment is executed at the front from the lower stop to the center position. If the seat has moved the inclination, adjustment does not take place.

- Backrest inclination, by the front passenger backrest angle adjustment motor (M28/5).
The backrest is adjusted from a backrest angle > 28° from the front stop into a 'more upright' position. This serves to provide a more favorable seat position. If the armrest is < 28° adjustment does not take place.

Adjustment of front passenger seat with occupant not strapped in
If the front passenger is not belted, positions are moved to that are matched to safety-relevant unfavorable conditions:
- Backrest inclination
The backrest is adjusted as of a backrest angle > 20° from the front stop. If the armrest is < 20° adjustment does not take place.

- Seat inclination
The seat is adjusted to the lower stop.

- Longitudinal seat position
If the seat is positioned too far back, it is moved forward (approx. s = 100 mm away from the rear stop).

Automatic adjustment of the front passenger seat can be interrupted at any time by operating the front passenger seat adjustment switch group with memory (S92).

If after manual adjustment the PRE-SAFE situation remains active, the front passenger seat is no longer adjusted by PRE-SAFE.

The adjustment process lasts until:
- the target area is reached (front passenger seat in ideal 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 front passenger seat adjustment switch group with memory if necessary.

Function sequence for closing all door windows
Closing the windows with PRE-SAFE should help to prevent objects from penetrating the vehicle interior in the event of an accident, body parts (e.g. arms) of the occupants from protruding out of the vehicle or occupants who are not belted from being catapulted out of open windows.

PRE-SAFE status signals are sent via the central gateway control unit to the following control units:
- Left front door control unit (N69/1)
- Right front door control unit (N69/2)
- Front SAM control unit (N10)

The windows are closed by the left front power window motor (M10/3), right front power window motor (M10/4), left rear power window motor (M10/5) and the right rear power window mot (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 is then extracted.

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:
- The power window switch group and driver outside mirror adjustment (S20/1)
- The front passenger power window switch (S21/2)
- The left rear power window switch (S21/3)
- The 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 [SHD] (with code (414) Power glass tilting/sliding roof) or automatic closing of panoramic sliding sunroof (on model 251 with code (413) Panoramic sliding sunroof with top sliding sunroof)
The purpose of closing the tilting/sliding roof or the panoramic sliding sunroof via PRE-SAFE is to prevent objects from entering the vehicle interior or body parts (e.g. arms) of the occupants from protruding out of the vehicle if an accident occurs.

The central gateway control unit transmits the PRE-SAFE status signals via the interior CAN to the overhead control panel control unit (N70).

The receipt of "PRE-SAFE situation detected" generates an internal "Move to PRE-SAFE position" request in the overhead control panel control unit.

The roof is closed to a gap of s = 50 mm over the tilting/sliding roof (SR [SHD]) drive unit (M12) (with code (414) Power glass tilting/sliding roof) or over drive unit 1, panoramic sliding sunroof (M12/6) (with model 251 with code (413) Panoramic glass sunroof with top sliding sunroof) and drive unit 2, panoramic sliding sunroof (M12/7) (with model 251 with code (413) Panoramic glass sunroof with top sliding sunroof), to ensure that in the event of any subsequent impact the smoke particulates generated by the pyrotechnical restraint equipment are then extracted.

Closing can be aborted at any time by manually operating the roof switch (N70s1).

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 indicated on the multifunction display (A1p13) in the instrument cluster (A1).

The message is: "PRE-SAFE UNAVAILABLE - SEE OPERATOR'S MANUAL"

Faults of other components that are part of the PRE-SAFE system are not displayed as PRE-SAFE faults.

Function sequence for ending PRE-SAFE
PRE-SAFE is disabled as soon as a PRE-SAFE situation no longer exists.

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. It is irrelevant here whether the vehicle is braking, accelerating, driving through a bend or if several such driving situations occur simultaneously.

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.