COLLISION PREVENTION ASSIST function

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Function requirements, general

 COLLISION PREVENTION ASSIST activated in the "Assistance" menu of the instrument cluster

 No undervoltage or overvoltage

 COLLISION PREVENTION ASSIST coded in electronic ignition lock control unit

 Engine running or drivetrain operational.

 The soiling and function test of the radar sensor has been completed successfully

 Vehicle is not in backward movement

 The CDI control unit or the ME-SFI [ME] control unit sends the signal "Engine running" or the "Drivetrain operational" signal via the chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit.

COLLISION PREVENTION ASSIST, general

The COLLISION PREVENTION ASSIST is an AWF that warns the driver optically and acoustically about a possible collision (e.g. a rear-end collision) with an obstacle or with the vehicle driving immediately ahead. Output of these warnings takes place in a vehicle speed range of v = 7 km/h up to the maximum speed of the vehicle. Control occurs by means of the COLLISION PREVENTION ASSIST controller unit.

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

 Radar sensor

 Control unit

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

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The COLLISION PREVENTION ASSIST comprises the following subfunctions:

 Function sequence for AWF

 Function sequence for braking assistance

Function sequence for AWF

COLLISION PREVENTION ASSIST is released manually through the operation level in the instrument cluster. The IC transmits the appropriate status via chassis CAN 2, the electronic ignition lock control unit and chassis CAN 1 to the COLLISION PREVENTION ASSIST controller unit. The COLLISION PREVENTION ASSIST controller unit performs a dirt and function test after every engine start. The function test requires an object in the detection area of the radar sensor system which is used by the COLLISION PREVENTION ASSIST controller unit as a reference value. If malfunctions are established or if no function test is possible then the COLLISION PREVENTION ASSIST cannot be activated.

The integrated radar sensor operates in the 25 GHz frequency range and detects objects in front of the vehicle. The detection angle is  = 18° 8° for s = 0 to 80 m.

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

 Direction of travel and vehicle speed

 Steering wheel angle

Direction of travel and vehicle speed:

The direction of travel is determined over the wheel rotation direction of the wheels. The vehicle speed is calculated on the basis of the wheel speeds. The wheel rotation direction and wheel speed for each individual wheel is recorded by the rpm sensors. The Electronic Stability Program control unit directly reads in the signals of the rpm sensors and sends them 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 directly reads in data from the steering wheel angle sensor and transmits it to the COLLISION PREVENTION ASSIST controller unit via chassis CAN 1.

The COLLISION PREVENTION ASSIST controller unit calculates the distance from the obstacle and the time up to a possible collision. The distance warning system 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 optically. If the time gap to the vehicle directly ahead goes below t = 0.8 s in flowing traffic (e.g. at a speed of v = 100 km/h, distance about s = 22.2 m), the COLLISION PREVENTION ASSIST controller unit transmits the request to output the warning via chassis CAN 1, electronic ignition lock control unit and chassis CAN 2 to the IC, which reacts by directly actuating the COLLISION PREVENTION ASSIST 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, electronic ignition lock control unit and chassis CAN 2 to the IC, which reacts by actuating the COLLISION PREVENTION ASSIST 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.

Timely warnings of obstacles ahead will only occur if a vehicle speed of v = 72 km/h is not exceeded.

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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 emergency braking is defined over the actuation speed and the actuation strength with which the brake pedal is actuated.

The COLLISION PREVENTION ASSIST controller unit also uses data from the radar sensor and calculates the necessary brake servo assistance while taking account of the distance and the closing speed to the obstacle. The COLLISION PREVENTION ASSIST controller unit transmits the appropriate requests 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. If there is no actuation or the intensity of actuation of the brake pedal by the driver reduces, the brake servo assistance on the driver braking is reduced and the Brake Assist System is deactivated. The Brake Assist System will also be deactivated if the driver presses the accelerator pedal.

 The detailed description of this PRE-SAFE® function can be found in the separate function description for the "PRE-SAFE® function".