Accuracy requirements for the road friction coefficient estimation of a friction-adaptive automatic emergency steerassist (ESA)

Abstract The number of traffic accidents resulting in personal injury and property damage is increasingly beingreduced by effective advanced driver assistance systems (ADAS). Nevertheless, many traffic accidentsstill cannot be prevented today because they are due to wet, snow- and ice-covered roads. For this reason, the Institute of Automotive Engineering (IAE) of the Technical University of Braunschweigis investigating the road friction coefficient sensitivity and adaptation of advanced driver assistance systems (ADAS) currently in series production from 2018 to 2021 as part of the ‘Road Condition Cloud’ research project funded by the German Research Foundation (DFG) in order to increase driving safety,particularly on wet, snow- and ice-covered roads. In this article, the road friction coefficient sensitivityand adaptation of an automatic emergency steer assist is simulatively investigated. This assist overridesthe driver to automatically execute an evasive maneuver. The driving maneuver used is a standardizedobstacle-avoidance maneuver that is simulatively repeated on a dry, wet, snow- and ice-covered road.The road friction coefficient sensitivity shows that this test is already failed on a wet road because thesimulated vehicle does not pass the second lane without errors. Subsequently, a road friction coefficientadaptation of the emergency steer assist is investigated. This adaptation varies the maximum lateralacceleration of the evasive trajectory depending on an estimated value of the road friction coefficientin order not to exceed the maximum adhesion coefficient of the wheels during the evasive maneuver.Ideally, the estimated value matches the true road friction coefficient so that the second lane is passedwithout errors even on a wet, snow- and ice-covered road. In contrast, an existing difference determineswhether the test is passed. Finally, the necessary accuracy requirements of the road friction coefficientestimation are determined in an novel estimation error diagram. A road friction coefficient adaptationincreases the driving safety of driver advanced assistance systems (ADAS) that are in series productiontoday and future highly automated driving functions (HAF) and is necessary for automated drivingbecause the driver is not present as a fallback level.