F2008-08-155
From Brake Assist to Autonomous Collision Avoidance
Advanced driver assistance systems cover an increasing number of functions to improve driver comfort and to reduce accidents and fatalities. In case of collision mitigation, the first brake assist systems achieved an accelerated brake force build up only depending on the drivers pedal behaviour. Today, collision mitigation systems that are already available in premium vehicles are using distance sensors like Radar or Lidar, too. Based on previous knowledge a more sophisticated collision mitigation strategy is possible. These distance sensor based systems calculate the danger potential depending on position- and relative speed information of other objects. This sensor information is sufficient to prepare the brake for an intervention or activate the brake with a limited brake force. For a maximal brake intervention, in particular on standing objects, single sensor information does not provide the necessary confidence in the relevancy of the environmental information. The system still needs the check for plausibility by regarding the driver´s acceleration- and braking behaviour. To wait for a driver reaction sometime means that valuable time elapses until a full brake intervention is possible. To reduce the need for this late plausibility more autonomous and with this quicker brake functions have to be realised, requiring highest signal confidence of the environmental detection. Fusion of different kind of sensors promises a way to reach this confidence. The article shows different possibilities to combine the information of 77Ghz radar and CMOS camera sensors, with the resulting modularity and computation power. High-level fusion combines relevant objects with interfaces, enabling modular hard- and software structures while fusing less pre-processed data like radar reflexions with 3D images delivers a better model of the environment. Further, the article shows the brake system requirements for advanced driver assistance systems and the ability of existing brake systems like active booster- or electro hydraulic brake systems, to meet these requirements. Main requirements for comfort functions are noise topics, while safety systems have to provide a sufficient brake force without getting the drivers pedal force. At higher differential speed to an obstacle, avoiding a crash by steering is later possible than avoiding it by brake intervention. This means that to reduce unintended brake interventions an autonomous working brake function has also to assess with free space analysis, if avoidance by steering is still possible. This result has to be included into the decision for braking. Continental equipped a test vehicle with ARS300 radar and CSF200 camera systems, an external controllable brake system, a fusion algorithm and a brake strategy for collision avoidance. The article shows the results of this autonomous active brake system at approaching speeds between 20 und 110kph.
Session: Advanced Safety Systems III