Search Results

This paper describes validation work carried out for two vehicle dynamics computer simulation programs. One program, referred to as VDANL (Vehicle Dynamics Analysis NonLinear), is intended to simulate passenger cars, vans and light trucks. The second program simulates All Terrain Vehicles (ATVs) and is referred to as NLATV (NonLinear ATV). The programs have been checked out and validated for a variety of maneuvering conditions and a broad range of vehicles. The programs run on IBM-PC/MS DOS compatible computers, and numerical methods have been used to give numerically stable solutions with reasonable computational speed over a broad range of maneuvering situations.

Lateral/directional dynamics involve vehicle yawing, rolling and lateral translation motions and dynamic stability concerns directional behavior (i.e. spinout) and rollover. Previous research has considered field test and computer simulation methods and results concerning lateral/directional stability. This paper summarizes measurements and simulation analysis of a wide range of vehicles regarding directional and rollover stability. Directional stability is noted to be strongly influenced by lateral load transfer distribution (LTD) between the front and rear axles LTD influences tire side force saturation properties, and should be set up so that side forces at the rear axle do not saturate before the front axle under hard maneuvering conditions in order to avoid limit oversteer and spinout.

This paper considers ground vehicle lateral/directional stability which is of primary concern in traffic safety. Lateral/directional dynamics involve yawing, rolling and lateral acceleration motions, and stability concerns include spinout and rollover. Lateral/directional dynamics are dominated by tire force response which depends on horizontal slip, camber angle and normal load. Vehicle limit maneuvering conditions can lead to tire force responses that result in vehicle spinout and rollover. This paper describes accident analysis, vehicle testing and computer simulation analysis designed to give insight into basic vehicle design variables that contribute to stability problems. Field test procedures and results for three vehicles are described. The field test results are used to validate a simulation model which is then analyzed under severe maneuvering conditions to shed light on dynamic stability issues.

All Terrain Vehicle (ATV) lateral/directional handling and stability is predominantly affected by tire and load transfer characteristics, and the lack of a rear axle differential. The combined effect of these characteristics are surveyed in this paper through the use of steady state analysis and simple linear dynamic analysis over a range of vehicle characteristics and maneuvering conditions. Computer analysis results are also compared with field test data obtained with instrumented vehicles.

All Terrain Vehicles (ATVs) have unique design features, including low pressure tires, a solid rear axle (i.e., no differential), and a relatively high center of gravity compared to wheel track width, that exert significant influence on their lateral/directional handling and stability properties. In addition, rider weight is a reasonable proportion of vehicle weight and weight shift is used as an additional control means in combination with steering, throttle and braking. This paper describes a nonlinear, time domain simulation analysis of the transient lateral/directional response properties of ATVs with rider control. The simulation is derived from earlier automotive applications. A description of the analytic model and computer simulation are given along with validation comparisons of instrumented vehicle field test data and computer simulation runs.

This paper presents an analysis of driver/vehicle performance over a range of maneuvering conditions including accident avoidance scenarios involving vehicle limit performance handling. Driver behavior is considered in the same dynamic analysis terms as vehicle response in order to give appropriate closed-loop measures of total system maneuvering capability and handling stability. A driver control structure is developed along with closed-loop system stability constraints on model parameters over a wide range of vehicle maneuvering conditions. Example simulation runs are presented for several accident avoidance scenarios.

This paper presents simple linear and non-linear dynamic models and numerical procedures designed to permit efficient vehicle dynamics analysis on microcomputers. Vehicle dynamics are dominated by tire forces and their precursor input variables, and a few inertial and suspension properties. The steady state and dynamic models discussed herein include a comprehensive, unlimited maneuver tire model with relatively simple vehicle suspension kinematics and inertial dynamics to cover the full vehicle maneuvering range from straight running to combined limit cornering and braking or acceleration. An attempt was made to minimize the required tire and vehicle model parameter set and to include easily obtainable parameters. The computer analysis procedures include: A steady state model for determining perturbation side force coefficients, and a stability factor and maneuvering time constant for lateral/directional control.

This paper presents test methods and modeling procedures for identifying the directional handling characteristics of vehicles over the full maneuvering range from straight running to limit cornering and/or braking. The test procedures are designed to validate steady-state and dynamic response performance. The model parameters are derived from simple static tests of vehicle properties and tire parameters identified from tire machine tests. Current steady-state field test procedures validate the model response under cornering only conditions. Model analysis then extrapolates vehicle response under combined cornering and braking conditions. Some discussion is devoted to potential braking in a turn transient testing for more complete model validation.

A significant aspect of trailering safetyis the ability of a combination vehicle to stop with the same effectiveness as the tow vehicle alone. This paper describes the operation of electric and surge brake systems and presents analytical equations which can be used to predict stopping distances of these combinations as well as those trailers having no brakes. Comparisons are then made to full scale brake performance tests with seven different trailers. Problems are discussed and recommendations for a trailer-alone brake test procedure are given.

This paper presents an analytically based approach to specifying a maximum allowable hitch load for passenger cars pulling trailers. The change in tow car steady-state directional stability, i.e., understeer, is the basis for the specification. This handling parameter is a function of hitch load, lateral acceleration, tow car to trailer weight ratio, and the amount of load leveling applied by a Class III hitch. Using these variables an allowable hitch load range was defined as that which would insure positive tow car understeer up to and including 0.3 g cornering. Over 50 combination-vehicle configurations (using three tow car sizes and eight trailers) were then tested in order to validate and revise the analytical boundaries. Based on these results a tow car stability criterion derived from maximum hitch load considerations appears a valid format for the trailer user and/or manufacturer.

This paper provides approximate factors, measurement techniques, and test procedures that can be used to determine trailer stability. The recommended performance metric is damping ratio, or an equivalent cycle to half amplitude which is evaluated, via a pulse-steer procedure, at some reference speed. A minimum damping ratio criteria of 0.15 at 55 mph is suggested and compared to the results of recent full scale tests. The approach is useful in selecting a minimum value of hitch load (for various weight tow cars) that will insure a minimum acceptable level of trailer stability at highway speeds.