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PRE-SAFE brake, function - GF30.30-P-3340LE

ENGINES 156, 273, 275 in MODEL 216 up to 31.8.10 with CODE (233) Distronic Plus as of model year 2009/YoM 08 

ENGINES 156, 272, 273, 275, 642, 629 in MODEL 221 up to 31.8.10 with CODE (233) Distronic Plus as of model year 2009/YoM 08 

View of instrument cluster (A1) with PRE-SAFE brake activated 

Fig 1: View Of Instrument Cluster With Pre-Safe Brake Activated
G07587474Courtesy of MERCEDES-BENZ USA

Function requirements for PRE-SAFE brake, general 

PRE-SAFE brake, general 

PRE-SAFE brake (also called CMS (C  ollision M  itigation S  ystem)) is an additional function of Distronic PLUS, which supports the PRE-SAFE safety concept.

The PRE-SAFE brake continuously determines the potential danger of a rear-end collision and, if there is accident-critical situation, initiates appropriate collision warning and accident mitigation measures if necessary.

The data from the long and short range radar is used to continuously calculate the potential risk of a collision.

If a situation is registered as critical, an optical collision warning (DTR warning lamp) appears initially in the instrument cluster and an acoustic collision warning (intermittent acoustic signal) is emitted.

If the driver fails to react sufficiently, he is then prompted to act by an automatic partial braking process. The required longitudinal dynamic

PRE-SAFE measures (such as belt tightening, closing of all windows, adjusting the front passenger seat) are requested from the radar sensors control unit (SGR) (N62/1) by the ESP control unit (N47-5) or regenerative braking system control unit (N30/6) (for hybrid) at the same time.

Function sequence for PRE-SAFE brake 

The function sequence is described in the following steps:

Function sequence for an accident-critical situation 

At the current closing speed, the distance of the vehicle from a detected object (vehicle) is detected as critical for an imminent collision. The objects in question are all objects in front of the vehicle that have been detected at least once as moving at speeds (of the host vehicle) up to 70 km/h as well as stationary objects.

Function sequence for activation and deactivation of the PRE-SAFE brake 

The PRE-SAFE brake can be activated or deactivate via the left and right multifunction steering wheel button group (S110, S111) in the "Assistance" menu of the instrument cluster.

When the PRE-SAFE brake is actuated, the "proximity warning readiness indicator" is lit at the bottom left of the electronic speedometer (A1p8).

IMPORTANT Activation of the PRE-SAFE brake is dependent on the function (function requirements) of the radar sensor system.

Function sequence for PRE-SAFE brake actuation 

The PRE-SAFE brake is activated when a potential accident situation is detected. The situation assessment is based on time thresholds (in which an object in front of the host vehicle is detected as critical), according to which the remaining potential for braking and evasive maneuvers is calculated. The first threshold value leads to triggering of the optical warning (DTR warning lamp) and acoustic collision warning (intermittent acoustic signal).

Function sequence for automatic partial braking 

Apart from going below the second threshold value, any evasive maneuver or acceleration command on the part of the driver is taken into account for triggering automatic partial braking. According to sensor data and input signals the braking torque for the automatic partial braking is determined by the radar sensors control unit based on a speed-dependent characteristic.

The braking torque is sent over the chassis CAN (CAN E) to the ESP control unit which adjusts the brake pressure accordingly through the traction system hydraulic unit (A7/3). The braking torque is newly calculated in the process by the radar sensors control unit based on the current clearances and the closing speed and transmitted to the ESP control unit or the regenerative braking system control unit (for hybrid).

When the braking effect is measurable, PRE-SAFE longitudinal dynamic measures are also requested over the chassis CAN.

Function sequence for deactivation of PRE-SAFE measures after actuation 

Triggered PRE-SAFE measures are deactivated just as soon as the critical object is no longer a threat, or when the action of the driver (an acceleration command, a decrease in braking or a steering maneuver) leads the system to assume that deactivation is required.

  Component description for instrument cluster A1
Model 216.3, 221.0/1 except 221.095/195		 GF54.30-P-6000LE
Model 221.095/195 GF54.30-P-6000LEH
  Component description for regenerative braking system control unit N30/6
Model 221.095/195		 GF42.22-P-1100LEH
  Component description for ESP control unit N47-5
Model 216.3, 221.0/1 except 221.095/195		 GF42.45-P-5118LE
  Component description for radar sensors control unit N62/1 GF30.30-P-3301LE 
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