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COLLISION PREVENTION ASSIST PLUS, function - GF30.30-P-0018RF

MODEL 205, 253 with CODE 258 (COLLISION PREVENTION ASSIST) 

Fig 1: Collision Prevention Assist Plus Function Diagram
G10132897Courtesy of MERCEDES-BENZ USA

Function requirements, general 

IMPORTANT COLLISION PREVENTION ASSIST PLUS is released manually through the operation level in the instrument cluster. The instrument cluster sends the corresponding status via user interface CAN, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

IMPORTANT The CDI control unit or the ME-SFI [ME] control unit sends the signal "Engine running" or "Drivetrain operational" via the drive train CAN, powertrain control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

COLLISION PREVENTION ASSIST PLUS, general points 

The COLLISION PREVENTION ASSIST PLUS continuously checks the following distance to the vehicle driving immediately ahead, warns the driver optically and acoustically about any possible collisions (e.g. a rear-end collision) with other vehicles and helps to significantly reduce the risk of accident. In an imminent collision situation, the COLLISION PREVENTION ASSIST PLUS initiates autonomous partial braking. To do this the COLLISION PREVENTION ASSIST controller unit evaluates the traffic situation in front of the vehicle, the route immediately in front as well as the driver activity and constantly determines the risk potential of a possible collision. Output of these warnings takes place in a vehicle speed range of v = 7 km/h up to 250 km/h. If the driver reacts to the acoustic warning and brakes, he will be assisted in this by the adaptive Brake Assist. This calculates the required brake force amplification according to the situation. Autonomous partial braking is also initiated if there is no reaction from the driver to the warnings. In this way a possible collision can be avoided or at least its consequences can be reduced.

The following components are integrated in the COLLISION PREVENTION ASSIST controller unit:

IMPORTANT MODEL 205, 253

with CODE 258 (COLLISION PREVENTION ASSIST)

with CODE 299 (PRE-SAFE® system)

The COLLISION PREVENTION ASSIST PLUS supports the safety system PRE-SAFE®.

The following presentation shows the detection range of the integral radar sensor:

Fig 2: Overview Of Radar Sensor Detection Range - Shown On Model 205.0
G10132898Courtesy of MERCEDES-BENZ USA

Illustration of the principle of the detection range of the radar sensor, shown on model 205.0 

The COLLISION PREVENTION ASSIST PLUS comprises the following subfunctions:

Function sequence for distance warning 

Apart from data from the radar sensor, the COLLISION PREVENTION ASSIST controller unit also evaluates the following variables:

Direction of travel and vehicle speed:

The direction of travel is defined using the wheel rotation direction. The vehicle speed is calculated from the wheel speed. The Electronic Stability Program control unit transmits appropriate information via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

Acceleration/yaw rate:

The acceleration/yaw rate is detected by the acceleration sensor integrated into the Supplemental Restraint System control unit. The Electronic Stability Program control unit transmits appropriate values via the dynamics CAN, Electronic Stability Program control unit, suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

Steering wheel angle:

The steering wheel angle sensor detects/records the steering wheel angle. The steering column tube module control unit directly reads in the signals from the steering wheel angle sensor and sends them via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit. The data from the steering wheel angle sensor serve to test the plausibility of the yaw rate detected by the acceleration sensor.

Accelerator pedal position:

The CDI control unit or the ME-SFI [ME] control unit sends information about the accelerator pedal position via the drive train CAN, powertrain control unit and the periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

Brake pedal position:

The Electronic Stability Program control unit transmits information about the position of the brake pedal via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

Setting the turn signal (turn signaling)

The steering column tube module control unit directly reads in the switch position of the combination switch and sends them via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit. The COLLISION PREVENTION ASSIST controller unit calculates the distance from the obstacle and the time up to a possible collision. The COLLISION PREVENTION ASSIST controller unit differentiates here between a static (without code 494 (USA version)) and a collision-critical distance warning.

Static distance warning (except code 494 (USA version)):

Output of the static distance warning takes place purely optically. If the distance from the vehicle directly ahead goes below t = 0.8 s in flowing traffic and this critical distance is maintained for t > 3 s (e.g. at a speed of v = 100 km/h, distance about s = 22.2 m), the COLLISION PREVENTION ASSIST controller unit sends the request to output the warning via the periphery CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster. The instrument cluster reacts by actuating the DISTRONIC warning lamp.

Collision critical distance warning:

Output of the collision-critical distance warning takes place optically and acoustically.

If an obstacle within the detection range of the radar sensor is classified as accident-critical (a collision will occur within t < 2.6 s), the COLLISION PREVENTION ASSIST controller unit sends the request to output the warning via the periphery CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which reacts by directly activating the DISTRONIC warning lamp and the IC speaker (intermittent tone).

The warning output cannot be acknowledged. Take-back of the warning only occurs if the situation has been defused.

For output of the warning the COLLISION PREVENTION ASSIST controller unit also takes the driver activity and the route directly ahead into account along with the vehicle speed and the distance to an obstacle. The vehicle moving directly ahead is detected through modifications of the accelerator pedal position, through actuation of the turn signal or through pressing the brake pedal. The route ahead is defined over the yaw rate, the steering wheel angle and the direction of travel.

The AWF can react to obstacles directly ahead up to a ground speed of v = 250 km/h, or to stationary obstacles up to about. v = 70 km/h, for example halting or parking vehicles.

System limits:

The collisions critical warning is not issued for a collision with:

Warning indicator in instrument cluster 

Fig 3: DISTRONIC Warning Lamp Instrument Cluster Display
G10132899Courtesy of MERCEDES-BENZ USA

Function sequence for braking assistance 

If the driver then reacts to the collision-critical distance warning with an emergency braking maneuver, the Brake Assist System provides support for the best possible utilization of the braking distance to the obstacle. The brake support is available in a vehicle speed range of v 7 km/h up to v 250 km/h.

The COLLISION PREVENTION ASSIST controller unit evaluates the data from the radar sensor and permanently calculates the required brake force.

IMPORTANT The hazard braking is defined over the actuation speed and the actuation strength with which the brake pedal is actuated. The actuation speed and the actuation forces are detected by front axle brake pressure sensor. The Electronic Stability Program control unit directly reads in the signals from the front axle brake pressure sensor, calculates the braking torque requested by the driver and sends this information via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the COLLISION PREVENTION ASSIST controller unit.

In the case of emergency braking the COLLISION PREVENTION ASSIST controller unit sends the relevant braking force via the periphery CAN, electronic ignition lock control unit and suspension FlexRay to the Electronic Stability Program control unit which actuates the hydraulic brake pressure via the traction system hydraulic unit. For vehicles with code 299 (PRE-SAFE® system) the PRE-SAFE® function implemented in the Electronic Stability Program control unit evaluates the currently requested braking torque and, if necessary, initiates appropriate measures.

IMPORTANT MODEL 205, 253

with CODE 258 (COLLISION PREVENTION ASSIST)

with CODE 299 (PRE-SAFE® system)

If a collision is unavoidable, occupant protection measures are taken in addition to intervention by the brake system.

If there is no actuation or the intensity of actuation of the brake pedal by the driver considerably decreases, the brake boost on the driver braking is reduced and the Brake Assist System is also deactivated. The Brake Assist System will also be deactivated if the driver presses the accelerator pedal.

The adaptive Brake Assist can react to stationary obstacles up to a vehicle speed of about. v = 70 km/h.

Additional function requirements for autonomous partial braking 

Function sequence for autonomous partial braking 

If the driver fails to react in an accident-critical situation to the warning, the COLLISION PREVENTION ASSIST controller unit initiates autonomous partial braking and a reduction in engine torque. The COLLISION PREVENTION ASSIST controller unit calculates the 2 braking torque required (average deceleration approx. a = 6 m/s) taking the following variables into account:

The COLLISION PREVENTION ASSIST controller unit sends the corresponding request to increase the braking torque and to reduce engine torque via the periphery CAN, electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit. The Electronic Stability Program control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and sends the request to reduce engine torque via the chassis FlexRay, powertrain control unit and the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit.

If the driver then reacts to the autonomous partial braking and brakes, the Adaptive Brake Assist System provides support for the best possible utilization of the braking distance to the obstacle.

IMPORTANT MODEL 205, 253

with CODE 258 (COLLISION PREVENTION ASSIST)

with CODE 299 (PRE-SAFE® system)

If a collision is unavoidable, occupant protection measures are taken in addition to intervention by the brake system.

Electrical function schematic for COLLISION PREVENTION ASSIST PLUS PE30.30-P-2065-97FBA 
Overview of system components for driver assistance systems GF54.00-P-9998RF
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