Abstract
KEYWORDS –vehicle, lateral, dynamics, relaxation, knc
ABSTRACT –
The lateral relaxation behavior of the chassis is an essential part of the transient overall vehicle performance. It describes the transient buildup of the lateral force in the contact area of the tire as a result of a steering wheel angle input considering the properties of the steering system, the kinematic and elastokinematic properties of the chassis as well as the transient tire characteristics. The aim of this study is to develop an analytical description of this process and to identify the most relevant system properties and their potential to improve the relaxation behavior of the chassis. Based on measurements on a kinematics and compliance test rig as well as on a dynamic axle test rig with an outer drum, a passive nonlinear quarter vehicle model is developed and validated. With the help of this model the most relevant system properties to the relaxation behavior of the chassis are identified: the influence of the subsystem steering gear on the transient kinematic steering angle, the steer angle due to lateral force and torque around the steering axis, the kinematic camber angle, the camber angle due to lateral force, and the tire characteristics. A linear analytical description deduced from the developed nonlinear model is validated and used to show the potential of improving the transient buildup of the lateral force by the variation of the identified parameters. Specifically, the stiffness of the camber angle against lateral force and combining the variation of the stiffness of the steer angle against lateral force and the variation of the steering ratio are identified as suitable chassis parameters to reduce the delay between a steering wheel angle input and the reaction of the lateral force in the contact area of the tire. Thus in the present study, for the first time the properties of the steering system, the tire characteristics and the kinematic and elastokinematic chassis properties are merged in one analytical description that allows understanding and comparison of their impact on the transient buildup of the lateral force in the contact area of the tire.