Collision Warning System, Basic Function - GF54.70-S-9900A
Model All (Light transporter)
Overview
This document contains information on:
- General
- Function requirements
- Function
- Static distance warning with insufficient distance
- Dynamic distance warning with risk of collision
- System limits
- Support from Active Brake Assist
- Autonomous partial braking
General
The collision warning system continuously checks the safe distance to the vehicle immediately in front and warns the driver optically and acoustically of potential collisions (e.g. rear-end collision) with other vehicles, thereby significantly reducing the risk of an accident. In an imminent collision situation, the collision warning system initiates autonomous partial braking if necessary.
To do this, the collision warning system radar sensor evaluates the traffic situation in front of the vehicle, the route immediately in front as well as the driver activity and continuously 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 design speed. If the driver responds to the warning tone and brakes, they will be supported in this (depending on the equipment) by the Active Brake Assist. This calculates the required brake force boosting 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 its consequences can at least be reduced.
The following component parts are integrated into the collision warning system radar sensor:
- Radar sensor
- Controller unit
The following presentation shows the detection range of the integral radar sensor.
Illustration of the principle of the detection range of the radar sensor
Function requirements
- Engine running or drivetrain 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 evaluates the data from the radar sensor and the multifunction camera. 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.
Apart from data from the radar sensor, the collision warning system radar sensor evaluates the following variables:
- Direction of travel and vehicle speed
- Acceleration/yaw rate
- Steering wheel angle
- Driver activity:
- Accelerator pedal position, accelerator pedal module
- Brake pedal position, from brake light switch
- Setting of the turn signal light (turn signaling), combination switch
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. This is displayed in the form of a visual warning in the instrument cluster. 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 via the instrument cluster. A dynamic distance warning can be output as of a vehicle speed of approx. 7 km/h.
The collision warning system radar sensor calculates the distance to the obstacle and the time to a possible collision. The radar sensor collision warning system differentiates here between the following warnings:
- Static distance warning
- Collision-critical distance warning:
Static distance warning
Output of the static distance warning takes place purely visually via the instrument cluster.
Collision-critical distance warning:
Output of the collision-critical distance warning takes place visually and acoustically via the instrument cluster.
The warning output cannot be acknowledged. Take-back of the warning only occurs if the situation has been defused.
To output the warning, the collision warning system radar sensor gives consideration to the driver's activity and the likely route in addition to the vehicle speed and the distance to an obstacle.
The driver's activity is detected, for example, through changes to the accelerator pedal position, through actuation of the turn signal lights or through pressing of the brake pedal. The route ahead is defined via the yaw rate, the steering wheel angle and the direction of travel.
In the case of stationary obstacles, a warning is only promptly output in the vehicle speed range between v ≥ 7 to approx. 70 km/h.
System limits
The collision-critical warning is not issued for a collision with the following objects or obstacles:
- Persons or animals
- Oncoming vehicles
- Cross traffic
- Curves in the road
Support from Active Brake Assist
To ensure the best possible utilization of the braking distance to the obstacle, the driver is supported with maximum full-stop braking from the Active Brake Assist when reacting to the collision-critical distance warning. Support from Active Brake Assist is available in a vehicle speed range of v ≥ 7 km/h up to the maximum design speed.
The collision warning system radar sensor evaluates the data from the radar sensor and continuously calculates the necessary brake force.
The maximum full-stop braking is defined via the actuation speed and the actuation strength with which the brake pedal is actuated.
The actuation speed and the actuation forces are detected by the master brake cylinder brake pressure sensor. The ESP® control unit reads in the signals from the master brake cylinder brake pressure sensor directly, calculates the braking torque requested by the driver, and sends this information to the collision warning system radar sensor.
In the event of maximum full-stop braking, the collision warning system radar sensor sends the necessary brake force to the ESP® control unit, which controls the hydraulic brake pressure via the traction system hydraulic unit. In vehicles with PRE-SAFE®, the "PRE-SAFE®" function implemented in the ESP® control unit evaluates the braking torque currently being requested and initiates appropriate measures if necessary.
If a collision is unavoidable, occupant protection measures are taken in addition to brake application.
If there is no actuation or the intensity of actuation of the brake pedal by the driver is significantly reduced, the brake force boosting on the driver braking is reduced and the brake force boosting is deactivated. If the driver presses the accelerator pedal, the brake force boosting is also deactivated.
Additional function requirements for autonomous partial braking for collision avoidance
- Vehicle speed: v = 7 to 70 km/h (to obstacles in front) or v = 7 to 30 km/h (to stationary obstacles)
Autonomous partial braking
If the driver fails to react to the collision-critical warning, the collision warning system radar sensor initiates autonomous partial braking and reduction in engine torque. The collision warning system radar sensor calculates the braking torque required (maximum deceleration approx. a = 6 m/s2 ), taking the following variables into account:
- Speed difference relative to the vehicle or obstacle
- Distance from vehicle or obstacle
The collision warning system radar sensor transmits the corresponding request to increase the braking torque and to reduce the engine torque to the ESP® control unit. The ESP® control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and sends the request to reduce the engine torque to the combustion engine control unit.
To ensure the best possible utilization of the braking distance to the obstacle, the driver is supported by brake force boosting when reacting to the autonomous partial braking.
If a collision is unavoidable, occupant protection measures are taken in addition to brake application.
| Function schematics | |||
| Collision warning system, function schematic | Model 420 with code BA3 (Active Brake Assist System) | PE54.70-S-2500-97VRA | |
| Model 447 with code BA3 (Active Brake Assist System) with code XM7 (MOPF II) | PE54.70-S-2500-97A | ||
| Additional basic functions | |||
| Brakes, basic function | GF42.00-S-9900A | ||
| Traffic area monitoring, basic function | GF54.71-S-1000A | ||
| Intelligent driving radar sensor, basic function | Model all (Light transporter) with code BA3 (Active Brake Assist System) with code ET4 (Active Distance Assist DISTRONIC) with code JA7 (Blind Spot Monitoring) |
GF54.71-S-2005A | |
| Front multifunction camera, basic function | Model all (Light transporter) with code BA3 (Active Brake Assist System) with code JA3 (Intelligent body control.) with code JA9 (Traffic Sign Assist) with code JB4 (Active lane keeping Assist) with code JW5 (Lane keeping assist) with code LG2 (LED Intelligent Light System) |
GF54.71-S-9890A |