Collision Prevention Assist Plus, Function - GF30.30-P-0018RDM

Model 172.4 

as of model year 2017 

with code 258 (COLLISION PREVENTION ASSIST) 

Courtesy of MERCEDES-BENZ USA

Shown model 172 

Function requirements for COLLISION PREVENTION ASSIST PLUS general points 

• COLLISION PREVENTION ASSIST coded in front SAM control unit
• COLLISION PREVENTION ASSIST controller unit coded
• IC coded
• No undervoltage or overvoltage
• Engine running or drivetrain operational
• Vehicle is not in backward movement
• Dirt and function test of the radar sensor in the COLLISION PREVENTION ASSIST controller unit completed successfully
• The COLLISION PREVENTION ASSIST PLUS is switched on in the "Assistant" menu of the IC

The COLLISION PREVENTION ASSIST controller unit (with CODE 258 (COLLISION PREVENTION ASSIST)) carries out a soiling and function test after every engine start. The function test requires an object to be located in the detection area (this object is used as a reference value). If malfunctions are established or if no function test is possible, the COLLISION PREVENTION ASSIST PLUS cannot be activated.

Switching on of the COLLISION PREVENTION ASSIST PLUS is occurs manually over the operation level in the instrument cluster. The IC transmits the appropriate status via chassis CAN 2 the SAM. control unit at the front and chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit.

The ME-SFI [ME] control unit (gasoline engine) or the CDI control unit (diesel engine) the sends the signal "Engine running" or "Drivetrain operational" via chassis CAN 1 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 the maximum speed of the vehicle. 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 assembly parts are integrated in the COLLISION PREVENTION ASSIST controller unit:

• Radar sensor
• Control unit

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

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

Courtesy of MERCEDES-BENZ USA

Illustration of the principle of the detection range of the radar sensor 

The COLLISION PREVENTION ASSIST PLUS comprises the following subfunctions:

• Function sequence for distance warning 
• Function sequence for braking assistance 
• Function sequence for autonomous partial braking 

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
• Acceleration/yaw rate
• Steering wheel angle
• Driver activity:

• Accelerator pedal position
• Brake pedal position
• Setting the turn signal (turn signaling)

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 sends corresponding information via chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit.

Acceleration/yaw rate:

Acceleration and the yaw rate of the vehicle are detected by the turn rate sensor, the transverse and longitudinal acceleration and sent via CAN H to the Electronic Stability Program control unit. The Electronic Stability Program control unit transmits the respective values via chassis CAN 1 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 reads in the signals of the steering wheel angle sensor directly and transmits information to the steering wheel angle via chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit. The data from the steering wheel angle sensor serve to test the plausibility of the turn rate detected by the yaw rate sensor for lateral and longitudinal acceleration.

Accelerator pedal position:

The ME-SFI [ME] control unit (gasoline engine) or the CDI control unit (diesel engine) sends Information about the accelerator pedal position via chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit.

Brake pedal position:

The Electronic Stability Program control unit sends information about the position of the brake pedal via chassis CAN 1 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 transmit this via chassis CAN 1 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 (without 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 chassis CAN 1, the front SAM control unit and chassis CAN 2 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 a moving obstacle within the detection range of the radar sensor system is classified as accident-critical (a collision will occur within t < 2.6 s), the COLLISION PREVENTION ASSIST controller unit transmits the request to output the warning via chassis CAN 1, from SAM control unit and chassis CAN 2 to the IC, which reacts by actuating the DISTRONIC warning lamp and the warning buzzer (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, apart from the vehicle speed and the distance to a vehicle moving directly ahead. 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.

Due warning of stationary obstacles is only given in a vehicle speed range of approximately v > 7 to 70 km/h.

System limits:

The collision-critical warning is not output for the following events:

• Persons or animals
• Oncoming vehicles
• Cross traffic
• in curves

Warning indicator in instrument cluster 

Courtesy of MERCEDES-BENZ USA

This is shown inversely on the multifunction display (A1p13) i.e the distance warning readiness indicator is hidden when the distance warning function is active.

Function sequence for braking assistance 

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

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

The emergency 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 chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit.

In the event of an emergency braking maneuver the COLLISION PREVENTION ASSIST controller unit sends information about the required braking torque via chassis CAN 1 to the Electronic Stability Program control unit which actuates the hydraulic brake pressure over the traction system hydraulic unit At the same time the PRE-SAFE® function implemented in the Electronic Stability Program control unit evaluates the currently requested braking torque and initiates appropriate measures as necessary.

PRE-SAFE®: If a collision is unavoidable occupant protection system measures are taken in addition to the intervention by the brake system. Detailed information on the topic of occupant protection is available in a separate document.

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.

Additional function requirements for autonomous partial braking 

• Vehicle speed: v = 7 km/h up to 105 km/h (up to obstacles directly ahead) or v = 7 km/h up to 50 km/h (in the case of stationary obstacles)
• Driver belted

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 braking torque required (average deceleration approx. a = 6 m/s2) taking the following variables into account:

• Differential speed to vehicle or obstacle
• Distance from vehicle or obstacle

The COLLISION PREVENTION ASSIST controller unit sends the appropriate request to increase the braking torque and to reduce the engine torque via chassis CAN 1 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 chassis CAN 1 to the ME-SFI [ME] control unit (gasoline engine) or the CDI control unit (diesel engine).

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.

PRE-SAFE®: If a collision is unavoidable, occupant protection system measures are taken in addition to the intervention by the brake system. Detailed information on the topic of occupant protection is available in a separate document.