1991-09-01

An Investigation of a Road-Vehicle Directional Behavior Under Steady-State Conditions 911872

ABSTRACT

An investigation of a steady-state motor vehicle steering characteristics is presented. The parameters that influence the steering response (e.g., front/rear load distribution, front and rear tire cornering stiffnesses, and tire slip angles) are included in the analytical development of the tire-vehicle system. A set of handling diagrams are obtained which show the influence of the tire-vehicle system's design factors and motion variables on the vehicle steering behavior. These diagrams are obtained for both the linear and nonlinear ranges of tire operation.

THE PURPOSE OF THIS PAPER is to investigate the steady-state directional response of a vehicle negotiating a turn at a constant forward speed. The vehicle model, as shown in Fig. 1 includes yaw and sideslip motions, but not body roll and load transfer. Under the assumption of constant vehicle speed, the driving torque applied to drive wheels is assumed to be small, which permits all wheels to be treated as “free rolling” (i.e., the tire lateral forces are dependent only on the tire lateral slip). Under the assumption of small disturbances, the variation in the longitudinal forces during directional motions is negligible. Consequently, the vehicle does not experience any longitudinal acceleration, provided that the driving torque is in equilibrium with the resistance to forward motion. The resistance derives primarily from the aerodynamic drag and rolling resistance forces produced by the tires. The control input to the vehicle model consists of the relatively small steering-wheel angular displacement. Thus, small steering inputs do not cause any change in vehicle forward velocity. The assumed limitations are necessary for the analysis to remain relatively simple and easy to comprehend. These limitations also allow the primary factors influencing vehicle directional behavior to be determined.

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