| A control theoretic model of driver steering dynamics is developed which can serve as a useful tool in the simulation of various lateral driving tasks. Equations of motion for the vehicle are first developed, then simplified and linearized to a two degree of freedom bicycle model. The driver model is then developed which exhibits pursuit-preview and compensatory levels describing human guidance and control activity, respectively. The compensatory mode consists of low- and high-frequency compensation elements, which are based upon a structural model of the human operator. This structural representation contains a model of human neuromuscular dynamics, a central processing time delay, and employs feedback loops which represent proprioceptive sensing and equalization on the part of the human. The frequency response characteristics of the compensatory mode resemble the well-known crossover model of the human operator and are adjusted based on the hypothesis that the driver operates on lateral position deviation. Input to the pursuit-preview mode is hypothesized to be future lateral displacement command with respect to instantaneous position. While this input is shown to be proportional to smooth road curvature, it is flexible enough to be applicable to commands with nonsmooth and discontinuous curvature functions. To allow the simulation of driving tasks which involves large changes in vehicle heading, nonlinear road kinematics are included in the driver-vehicle model. The resulting model is then applied descriptive fashion to a pair of driving tasks for which data is available from a driving simulator, namely: (1) lane keeping on a curving roadway, and (2) an accident avoidance maneuver. Selection of parameters for the driver model is simplified to that of determining the crossover frequency for the compensatory mode, and the preview or advancement time for the pursuit-preview mode. The driver model is then exercised in predictive fashion in a handling qualities and stability evaluation of a lane keeping task on a curving roadway in which the vehicle possesses one of three different steering systems: a conventional front-wheel system or one of a pair of four-wheel systems. |
