GF30.30-P-3340SX Pre-Safe Brake, Function

GF30.30-P-3340SX PRE-SAFE Brake, Function
- with CODE (233) Distronic Plus
- as of 1.9.06 up to model year 08

Component Identification:

The PRE-SAFE brake (also known as the Collision Mitigation System (CMS)) is an additional function of DISTRONIC PLUS which supports the safety concept PRE-SAFE. The PRE-SAFE brake permanently determines the potential danger of a collision occurring and initiates appropriate measures to warn of an impending collision and possibly to mitigate the effects of a collision in critical situations.

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. Required longitudinal dynamic PRE-SAFE measures (such as tightening seat belts (for model 221), closing all windows, adjusting the front passenger seat) are requested at the same time.

Potential accident situation
The distance between the vehicle and a detected object is recognized to be critical for an imminent collision at the current closing speed. 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 requirements for PRE-SAFE brake
^ "Circuit 61 ON" (engine running)
^ CMS_AVL (PRE-SAFE brake) coded in central gateway control unit (N93)
^ Radar sensor system not disabled
^ Dirt/function test of the long range radar completed
^ ESP not deactivated
^ Parking brake not applied
^ Selector lever position "D"
^ PRE-SAFE brake activated in instrument cluster

Activation/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 menu "Assistance" of the instrument cluster.
When the PRE-SAFE brake is activated, the "distance warning system indicator" (1) at the bottom left next to the electronic speedometer (A1p8) is lit up.

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

Activation of PRE-SAFE brake
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).

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 (SGR) (N62/1) based on a speed-dependent characteristic.
The braking torque is transmitted via the chassis CAN to the ESP control unit (N47-5) which controls the brake pressure accordingly via the traction system hydraulic unit (A7/3). The braking torque is continuously recalculated by the radar sensors control unit on the basis of the current distance and the closing speed, and is relayed to the ESP control unit.

Once a braking effect is measurable, additional PRE-SAFE measures in the longitudinal direction are commanded via the CAN data bus.

Deactivation of triggered PRE-SAFE measures
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.