Vehicle Handling: Effects of Lateral Asymmetries on Turning Response, and Some Developments in Closed-Loop Control.

Abstract

The effects of several lateral asymmetries typically existing in passenger vehicles are studied using two different mathematical vehicle models: a non-linear three-degree-of-freedom model and a comprehensive seventeen-degree-of-freedom model. Equations describing the asymmetric configurations are developed. Response asymmetry measures and vehicle asymmetry parameters are defined and the sensitivity of the response to various types of asymmetries is determined for steady-state turns and a standard transient maneuver. It is found that: (i) typical levels of vehicle asymmetry can cause substantial response asymmetry in severe maneuvers, (ii) the simple model and complex model display similar response asymmetry except for vehicle configurations with substantial roll steer, (iii) tire asymmetry and off-center loading cause the greatest response asymmetry, (iv) the sensitivity of response to various asymmetry parameters is somewhat different in steady turning than in transient maneuvers. Closed-loop vehicle control is considered using a describing-function model of the human driver. This model is developed and programmed to follow a curved road path. A technique is developed for determining unique parameters for this model from measured or calculated yaw rate response data. Stability analyses are performed for a driver/vehicle system with altered vehicle parameters in both the frequency and time domains, the latter using the three-degree-of-freedom vehicle model. It is found that a major change in vehicle properties is required to cause instability. Closed-loop control of an asymmetric vehicle is investigated. It is found that typical asymmetry levels reduce system stability but do not cause instability.