Abstract

The conceptual design of the early warning based roll instability enhancement system is realized through systematic investigations on static and dynamic roll behavior of the vehicles, identification of indicators for the onset of instability, and reliability analysis. The relative and absolute roll instability criteria are initially derived from the rollover mechanics of different heavy vehicle combinations. The relative roll instability conditions are evaluated under steady cornering maneuvers through development and analysis of static roll plane models. The sensitivity of the static rollover threshold (SRT) measure to variations in design and operating factors of the vehicle and suspension configurations is evaluated and the conditions of relative rollover for different vehicle configurations are identified. A constant velocity three-dimensional model is derived for relative roll instability analysis of articulated vehicles under dynamic directional maneuvers. Dynamic rollover threshold of articulated heavy vehicles is proposed on the basis of effective lateral acceleration (ELA) and relative rollover criterion. The absolute roll instability of heavy vehicles is further investigated using energy approach to derive the absolute rollover limits. A number of potential rollover indicators are identified and evaluated for a five-axle tractor semi-trailer combination using the constant velocity three-dimensional vehicle model in terms of their reliability and early warning capability for driver's actions. The effectiveness of proposed indicators for the open-loop roll stability enhancement is investigated through development and analysis of a comprehensive vehicle model, incorporating braking dynamics. Time delays due to driver's reaction and the transportation lag of the braking system are characterized by a variable referred to as reaction delay. The rollover indicators are investigated for their effectiveness for open- loop roll stability control in various cornering and evasive maneuvers, road conditions, braking efforts, and reaction delays. The study revealed that the RSF is the most reliable indicator, irrespective of the vehicle configurations, while its measurability is relatively poor. The indicators based upon lateral acceleration, sprung and unsprung mass roll angles and steering velocity factor yield good correlation with RSF, but exhibit certain sensitivity to variations in design and operating factors