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This paper describes the driver/vehicle modeling aspects of a computer simulation that can respond to highway engineering descriptions of roadways. The driver model interacts with a complete vehicle dynamics model that has been described previously. The roadway path is described in terms of horizontal and vertical curvature and cross slopes of lanes, shoulders, side slopes and ditches. Terrain queries are made by the vehicle dynamics to locate tires on the roadway cross-section, and to define vehicle path and road curvature at some distance down the road. The driver model controls steering to maintain lateral lane position. Speed is maintained at a speed limit on tangents, and decreased as needed to maintain safe lateral acceleration. Because the bandwidth of longitudinal (speed) control is much lower than lateral/directional (steering) control, the driver model looks further ahead for speed control than for steering.

This paper reviews the development and application of a computer simulation for simulating ground vehicle dynamics including steady state tire behavior. The models have been developed over the last decade, and include treatment of sprung and unsprung masses, suspension characteristics and composite road plane tire forces. The models have been applied to single unit passenger cars, trucks and buses, and articulated tractor/trailer vehicles. The vehicle model uses composite parameters that are relatively easy to measure. The tire model responds to normal load, camber angle and composite tire patch slip, and its longitudinal and lateral forces interact with an equivalent friction ellipse formulation. The tire model can represent behavior on both paved and off-road surfaces. Tire model parameters can be automatically identified given tire force and moment test data.

This paper describes a low cost, PC based driving simulation that includes a complete vehicle dynamics model (VDM), photo realistic visual display, torque feedback for steering feel and realistic sound generation. The VDM runs in real-time on Intel based PCs. The model, referred to as VDANL (Vehicle Dynamics Analysis, Non-Linear) has been developed and validated for a range of vehicles over the last decade and has been previously used for computer simulation analysis. The model's lateral and longitudinal dynamics have 17 degrees of freedom for a single unit vehicle and 33 degrees of freedom for an articulated vehicle. The model also includes a complete drive train including engine, transmission and front and rear drive differentials, and complete, power assisted braking and steering systems. A comprehensive tire model (STIREMOD) generates lateral and longitudinal forces and aligning torque based on normal load, camber angle and horizontal (lateral and longitudinal) slip.

This paper describes and compares three methods of estimating the static rollover threshold of passenger cars and light trucks. The Static Stability Factor (SSF), Side Pull Ratio (SPR), and Tilt Table Ratio (TTR) “metrics” are described and methods of measuring each are presented. The comparison of the three metrics is limited to the accuracy, repeatability, and ease of the measurements, and does not attempt to compare their ability to predict real world rollover accident involvement. The results of the comparison have shown that the three metrics are very closely related. Based on this, the rollover accident predictive power of each metric is expected to be similar. However, the ease and accuracy of the TTR measurement make it the most useful of the three. DURING THE 1980's, the use of light trucks and multi-purpose vehicles for basic transportation increased considerably. By 1990, domestic full-size pickup trucks were regularly among the top five passenger vehicles sold.

This paper discusses the importance of having an adequate model for the dynamic response characteristics of tire lateral force to steering inputs. Computer simulation and comparison with experimental results are used to show the importance of including appropriate tire dynamics in simulation tire models to produce accurate predictions of vehicle dynamics. Improvements made to the tire dynamics model of an existing vehicle stability and control simulation, the Vehicle Dynamics Analysis, Non-Linear (VDANL) simulation, are presented. Specifically, the improvements include changing the simulation's tire dynamics from first-order system tire side force lag dynamics to second-order system tire slip angle dynamics. A second-order system representation is necessary to model underdamped characteristics of tires at high speeds. Lagging slip angle (an input to the tire model) causes all slip angle dependent tire force and moment outputs to be lagged.

This paper presents a methodology for validating vehicle stability and control computer simulations. Validation is defined as showing that, within some specified operating range of the vehicle, a simulation's predictions of a vehicle's responses agree with the actual measured vehicle's responses to within some specified level of accuracy. The method uses repeated experimental runs at each test condition to generate sufficient data for statistical analyses. The acquisition and reduction of experimental data, and the processing path for simulation data, are described. The usefulness of time domain validation for steady state and slowly varying transients is discussed. The importance of frequency domain validation for thoroughly validating a simulation is shown. Both qualitative and quantitative methods for the comparison of the simulation predictions with the actual test measurements are developed.