Effects Causing Untripped Rollover of Light Passenger Vehicles in Evasive Maneuvers

Abstract

Accident statistics show that rollover accidents contribute to a large proportion of fatal traffic accidents in the U.S.. In the past it has been documented that some light passenger cars showed tendencies to roll over in evasive lane change maneuvers. In 1997, a newly developed mini van rolled over in a severe double lane change test called moose-test. Recently (2001), a new SUV showed similar tendencies in the Consumers Union Short Course test. It is not immediately clear why these evasive test maneuvers are so strongly related to untripped rollover of light passenger vehicles. Therefore, the goal of current research is to understand the circumstances and effects causing modern passenger vehicles to roll over in evasive maneuvers on the road. This paper discusses research activities concerning the following questions: How do critical steering strategies lead to untripped rollover? Are resonant frequencies excited during maneuvers leading to rollover? What are the prerequisites for dynamic untripped rollover? To answer these questions, extensive testing with an instrumented test vehicle as well as simulations with a real-time capable vehicle dynamics simulation were performed. The results were validated with a near standard production SUV. Results show that rollover critical steering strategies are related to high differences in steering amplitudes and to high steering wheel angle rates. Critical steering frequencies are in the range of 0.3 to 0.8Hz. The time for counter steering during evasive maneuver tests is related to the maximum of roll rate and side slip angle. An excitation of the roll natural frequency does not play a roll in untripped rollover. The main conditions necessary for untripped rollover are to create high roll-rates and maximum side forces at both axles simultaneously. Therefore requisits are heavy side to side excitations of the body and dynamic, greatly increased wheel loads as well as a oversteering behavior of the vehicle.