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.
The modeling of driver/vehicle interaction involves both the basic dynamics of driver response and the adjustment of parameters to achieve closed loop control stability Basic driver response dynamics result from sensory/motor characteristics and adaptation to vehicle dynamics and task demands Modeling efforts in the past have ranged from simple feedback control to detailed, veridical models of driver perception, central processing, motor response and higher cognitive functions This paper presents path and speed control models formulated to accomplish tasks ranging from maintenance of cornering acceleration and lane position under curving road alignments to obstacle avoidance and control under emergency limit performance conditions Steering models for maintaining lane position under curved path conditions involve steering directly proportional to road curvature, and feedback control of lane position, heading and curvature errors Normal speed control entails throttle response to errors with respect to commands such as posted speed limits, curve warning signs, desired cornering acceleration or desired following distance from a lead vehicle Emergency obstacle avoidance maneuvering typically comprises simpler transient steering and/or braking processes These driver maneuvering models are described and demonstrated with a fully nonlinear vehicle computer simulation that includes a tire model with force saturation properties and appropriate interaction between lateral and longitudinal slip demands that are important m combined cornering and braking maneuvers Closed loop stability requirements are discussed, and the stability and control of the driver models are presented