Search Results

An efficient model for simulating articulated vehicle dynamics for yaw stability during heavy braking is developed. The system’s governing equations are derived using Lagrange’s Equations, eliminating the need for any assumptions concerning forces at the tractor-trailer hitch. Detailed parametric results are presented. Six important dimensionless parameter groups affecting yaw stability are identified. Parametric plots based upon numerical simulations, are presented and a yaw stability limit criterion is defined to evaluate the simulation results. The graphical results show that increasing trailer braking consistently increases stability, while increasing the trailer to tractor weight-ratio decreases stability assuming balanced tractor braking. The most influential parameter affecting vehicle stability is the trailer fore/aft C.G. position.

Comparison of a vehicle and its occupant's dynamic test response to analysis results for a low speed, in-line impact, are made. The methodology employed combines a previously validated two degree of freedom linear spring-mass-dashpot analytical solution for the vehicle, with the Articulated Total Body (ATB) numerical response for the occupant. Preliminary results, based upon a comparison with published test data, indicate that the simulation employed is capable of delivering reasonable peak-level acceleration results and approximate time intervals, once appropriate vehicle and occupant mass, stiffness, energy dissipation, seat back and occupant position data are input. Sensitivity of results to various vehicle and occupant parameters, such as seat-back stiffness, inclination and occupant back, head and neck sitting angles, are also presented.

A coordinated test and analysis program was conducted to determine whether a previously proposed, linear, analytical model could be adapted to simulate low speed impacts for vehicles with various combinations of energy absorbing bumpers (EAB). The types of bumper systems impacting one another in our program included, in various combinations; foam, piston and honeycomb systems. Impact speeds varied between 4.2 and 14.4 km/h (2.6 and 9.0 mph) and a total of 16 tests in 6 different combinations were conducted. The results of this study reveal that vehicle accelerations vary approximately linearly with impact velocity for a wide variety of bumper systems and that a linear mass-spring-damping model may be used to efficiently model each vehicle/bumper-system for low speed impacts.

This paper compares the analytical response of a low speed, in-line, vehicle impact with that of a simulated bumper test involving a rigid striker. Results from a previously validated analysis procedure indicate that a rigid pendulum mass impact test on a vehicle bumper, such as the one currently mandated by the federal government, yields significantly different results from that of a typical two-vehicle impact. This paper then proposes methods by which the existing government tests could be extended to yield additional design and analysis data that could be used to help design lower vehicle compartment loadings.