Collision warning system, basic function

Overview

This document contains the following information:

 General

 Function requirements

 Function

General

The collision warning system monitors the road space area ahead of the vehicle using the radar sensors behind the radiator grille or, depending on the equipment installed, using the multifunction camera behind the windshield. Using the movement profile, the multifunction camera is able to distinguish between pedestrians, cyclists and vehicles.

In the event of an imminent collision, the system warns the driver and, in an emergency, brakes autonomously. If the driver himself brakes, the system supports the brake request depending on the respective situation.

The sensitivity of the collision warning system can be adjusted in three stages.

Thanks to the extensive road space monitoring, not only collisions with vehicles ahead but also with vehicles crossing in front (depending on the equipment installed) can be avoided. The DISTRONIC PLUS and Active Brake Assist systems (vehicles without Driving Assistance Package) can detect pedestrians and cyclists with the aid of the multifunction camera (mono camera). Vehicles with Driving Assistance Package can also detect vehicles (multifunction camera (stereo camera)).

The end-of-tailback emergency braking function on vehicles with Driving Assistance Package brakes the vehicle if there is no possibility of avoiding a collision, and can in this way prevent accidents or minimize their severity.

Function requirements

 Engine running or drive train operational

 Collision warning system activated

 Vehicle not moving backward (defined by the direction of wheel rotation)

 Radar sensor soiling and function test completed

 Multifunction camera soiling and function test completed (depending on equipment installed)

 No tight bends

Function

The radar sensor and the multifunction camera (depending on the equipment installed) monitor the road space ahead of the vehicle.

Depending on the vehicle equipment, the controller unit in the radar sensor (vehicles without Driving Assistance Package) or the intelligent driving control unit (vehicles with Driving Assistance Package) evaluate the data from the two sensors. If a hazardous situation is detected, the system warns the driver of an imminent collision. If the situation worsens further, the system initiates autonomous braking.

The collision warning system is switched on each time the ignition is started. The driver can operate the system via the multimedia system.

The following settings can be made:

 "Early" setting: The intervention points have a very sensitive setting. This setting enables the highest possible safety by the system. In some situations, however, this may be considered obtrusive.

 "Medium" setting: The intervention points have the best possible configuration for maximum safety without obtrusive interventions. This setting is set automatically when the system has been switched off before an ignition change.

 "Late" setting: The intervention points are configured to occur significantly later. This setting should only be used in the case of a very sporty driving style.

 "OFF" setting: When switched off, the distance warning function and autonomous emergency braking is deactivated.

Static distance warning with insufficient distance

The static distance warning is output as soon as the time interval to a vehicle ahead drops below a certain value, i.e. the safe distance becomes too small. The warning is displayed visually in the form of a warning lamp. The static distance warning operates for moving objects in a vehicle speed range of 30 to 250 km/h.

Dynamic distance warning with risk of collision

The dynamic distance warning is triggered as soon as the vehicle approaches the vehicle detected ahead too fast or with excessive acceleration. In this case, both a visual warning and a warning tone are output. A dynamic distance warning can be output as of a vehicle speed of approx. 7 km/h.

Autonomous emergency braking

Autonomous brake application is initiated if the driver fails to react to the distance warnings. The vehicle is braked heavily. The consequences of a potential rear-end collision or of an accident involving pedestrians or cyclists who cross the road without due attention or who are overlooked by the driver are mitigated. The driver is also warned of the initiated braking operation by haptic means. Autonomous brake application can take place as of a vehicle speed of approx. 7 km/h.

At low vehicle speeds, autonomous brake application may be sufficient to avoid a rear-end impact or collision.

If the driver depresses the brake pedal during autonomous brake application, situation-based brake force boosting takes over and can decelerate the vehicle up to maximum full-stop braking.

If autonomous braking application or situation-based brake force boosting exceeds certain deceleration values, additional functions such as seat belt tensioning are activated.

Situation-based brake force boosting

Situation-based brake force boosting is triggered after the dynamic distance warning if the driver brakes significantly. Brake force boosting amplifies the brake pressure generated by the driver via the brake pedal.

The collision warning system brakes with the maximum possible deceleration up to the point of collision in order to reduce the impact velocity as far as possible.

Intervention by the situation-based brake force boosting function can be overridden by the driver at any time, i.e. if the driver wants to brake more heavily than the system intends, the driver's braking request has priority. The driver can cancel intervention at any time by releasing the brake, depressing the accelerator pedal or steering and thereby attempting to avoid the obstacle.

If the braking procedure exceeds certain acceleration values, PRE-SAFE® functions are also activated. Situation-based brake force boosting can take place as of a vehicle speed of approx. 7 km/h.

 If braking assistance or automated brake application has been canceled or completed, a display appears that indicates the system reaction.

End-of-tailback emergency braking function (vehicles with Driving Assistance Package)

The end-of-tailback emergency braking function detects end-of-tailback scenarios where there is either restricted or no evasive maneuvering possibilities. Here, the road space monitoring function defines the source of the risk of collision:

 Vehicle in own lane

 Vehicles in adjacent lanes

 Guardrails

In detected end-of-tailback scenarios where evasive steering is not an option, the collision warning system initiates early emergency braking, which can reduce the vehicle speed by up to 100 km/h. The end of traffic jam emergency braking function is active in a vehicle speed range of roughly 7 to 130 km/h.

Cornering emergency braking function (vehicles with Driving Assistance Package, as of market launch of model 167)

The cornering emergency braking function detects risks of collisions with oncoming vehicles when turning into an oncoming lane.

An autonomous brake application is only initiated if the vehicle was braked to a standstill before crossing over the lane marking.

The cornering emergency braking function is active in a vehicle speed range of roughly 2   to 10km/h.

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