Browse Topic: Rollover accidents
Electric vehicles (EVs) face unique safety challenges under pole side impact conditions, largely due to the presence of floor-mounted battery packs. Existing regulatory test procedures, such as FMVSS 214, primarily address occupant injury using full-height cylindrical obstacles. These procedures were originally developed for internal combustion vehicles (ICVs). However, real-world roadside crashes frequently involve obstacles of varying heights, such as guardrails, curbs, and median bases. While these obstacles pose limited risk to the passenger compartment, they can intrude into the battery pack and trigger thermal runaway. This study investigates the influence of obstacle height on EV pole side impacts. Finite element simulations of a commercially available sedan were conducted against rigid obstacles of different heights. Results reveal a non-monotonic trend of battery intrusion governed by the interplay between rollover dynamics and structural stiffness. Theoretical analyses were conducted to clarify the underlying mechanisms. When the obstacle height falls below the window frame level, rollover effects become more significant. The longer roll moment arm allows part of the impact energy to be dissipated through vehicle roll motion, leading to a reduction in battery intrusion. However, as the obstacle height is further reduced into the threshold beam and battery side beam region, the supporting structural members are bypassed. The equivalent contact stiffness drops sharply, resulting in significant battery intrusion. The findings demonstrate that obstacle height governs EV battery safety through a competition between rollover energy dissipation and reduced contact stiffness. This work provides new insights for extending existing side impact tests to low-height obstacles and offers guidance for vehicle safety design.
Vehicles with a high center of gravity (CG) and moderate wheel track, like compact Sport Utility Vehicles (SUVs), have a relatively low Static Stability Factor (SSF) and thus are inherently less stable and more susceptible to rollover crashes. Moreover, to be more maneuverable in highly populated urban areas, a smaller Turning Circle Diameter (TCD) is necessary. Here, Variable Gear Ratio (VGR) steering systems have major benefits over traditional Constant Gear Ratio (CGR) systems in terms of enhancing both roll stability and agility. To adapt VGR steering systems to a particular vehicle dynamic, Full Vehicle (FV) and Driver-in-the-Loop (DIL) simulations are utilized. Using this method, exact calibration is possible according to realistic driving conditions so that the VGR steering C-factor curve is properly tuned for optimal handling in on-center, off-centre, and transitional areas of the Steering Wheel Angle (SWA). Primary performance measures—e.g., SWA gradients at different lateral accelerations and C-factor changes for different SWA ranges—are examined in the DIL environment to maintain a natural feel during steering. In addition, DIL simulation allows a check on cycloidal curve character, manufacturing asymmetry, and its effect on total drive performance.
Armored vehicles offer limited view to the driver and crew. Two-dimensional vision-based situational awareness (SA) systems provide the driver a view of the area around the vehicle. The addition of distance to objects can offer a more comprehensive understanding of the surroundings assisting the driver with the locations of obstacles and rollover hazards. Methods currently available or under development for depth perception have issues limiting their utility in the field.. Some interfere with crew operations, others are are too costly, are not covert or require excessive processing. We offer a low-cost and computationally efficient approach called Kinetically Enhanced Situational Awareness (KESA) that derives distance to objects using existing SA sensors and processors combined with a knowledge of vehicle kinematics. We demonstrate how range can be used to enhance and supplement AI based driver assistance and threat warnings.
Dynamic rollovers represent a major hazard for helicopters during near-ground operations, often resulting in significant aircraft damage and passenger injuries. To improve safety in operations, recent studies have focused on developing a Helicopter Flight Data Monitoring framework to provide data-driven insights on operational safety. This work contributes to that effort by proposing an approach to identify precursors to dynamic rollovers. According to NTSB reports, approximately 60% of such incidents occur during in-flight phases like hover, hover-taxi, or landing. To capture the complex non-linear dynamics of helicopters, physics-based simulations were conducted to estimate a first hitting time metric, defined as the time until blade-ground contact, across a wide range of initial conditions for an inflight initial state of the helicopter. Eight parameters were identified as driving the first hitting time, and a probabilistic model was created to predict the distribution of that metric for different values of those parameters. Based on the predicted distributions, a risk-based metric was derived to robustly assess the risk of dynamic rollover and identify safer operational boundaries.
Vehicle navigation in off-road environments is challenging due to terrain uncertainty. Various approaches that account for factors such as terrain trafficability, vehicle dynamics, and energy utilization have been investigated. However, these are not sufficient to ensure safe navigation of optionally manned ground vehicles that are prone to detection using thermal infrared (IR) seekers in combat missions. This work is directed towards the development of a vehicle IR signature aware navigation stack comprised of global and local planner modules to realize safe navigation for optionally manned ground vehicles. The global planner used A* search heuristics designed to find the optimal path that minimizes the vehicle thermal signature metric on the map of terrain’s apparent temperature. The local planner used a model-predictive control (MPC) algorithm to achieve integrated motion planning and control of the vehicle to follow the path waypoints provided by the global planner. Vehicle apparent temperature-aware kinodynamic motion planning MPC was developed to minimize the vehicle thermal signature metric -- while respecting local mobility constraints due to the terrain grade to prevent vehicle rollover. Additionally, a surface energy model with the inclusion of a vegetation layer was developed to simulate the apparent temperature of the background terrain. The effectiveness of the developed algorithm is demonstrated for the scenario where the adversarial threat perspective is assumed to be from the top looking down at the vehicle.
Letter from the Special Issue Editors
ABSTRACT As a continuation of previous collaborative efforts between several US Army organizations and industry leaders which led to the procurement of a National Stock Number (NSN) for a near commercial-off-the-shelf winter tire/wheel assembly for the High Mobility Multipurpose Wheeled Vehicle (HMMWV), this study investigates a low-cost, postproduction modification known as ‘siping’ which may incrementally improve standard tires deployed on the Joint Light Tactical Vehicle (JLTV) in cold regions. Data from engineering tests will quantify performance differences as well as driver feedback from the 11th Airborne Division Soldiers in Alaska show moderate improvement from cutting razor-thin grooves known as ‘sipes’ on conventional winter tire sets. However, Army winter performance specifications developed in 2021 from HMMWV testing quantify greater available improvement to traction available, necessitating further development for winter traction in the JLTV family of tire sets as well as future procurements for additional Tactical Vehicles. Providing Soldiers with state-of-the-art winter tires which are effective at decreasing roll-over and other loss of control incidents increases safety and mobility in northern operations and is the objective of this research. Citation: Witte, C., et al., “Modifying Military Tires for Improved Winter Traction,” In Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 15-17, 2023.
The objective of this work is to capture the final deformed shape of a vehicle after a rollover caused by a corkscrew event (ramp). With this study, it will be possible to understand the vehicle structural behavior during this event and be able to improve the vehicle safety in this specific condition. For this proposal, it will be presented a virtual methodology using available commercial CAE tools and perform a crashworthiness analysis of the desired event. The first step is to capture the dynamic event through a Multibody analysis that represents the interaction among the vehicle tire, suspension components (Springs, Dampers, Jounce Bumper, Bushings, Stabilizer Bar etc.), vehicle structural stiffness, mass, center of gravity and inertias when exposed to a corkscrew standard ramp, that initiates the rollover event. This methodology will represent with fidelity all dynamic aspects of rollover event before the vehicle touches the ground. At this point, comparison of the analysis velocities output with experimental data can be achieved. After this step, a second non-linear structural analysis in the time domain, will be performed with the vehicle positioned, with all 6 DOF matrix velocities inputted from the Multibody analysis output, at the instant of time before touching the ground. Thus, it will be possible to capture the structural behavior and deformation when the vehicle hits the ground and rolls by itself. The final structure deformed shape will be compared with physical tests results.
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