Off-road Vehicle Dynamics

Abstract

A thorough understanding of vehicle dynamics is essential when designing high performance navigation systems for off-road vehicles. This section intends to provide readers with a comprehensive framework of the dynamics involved with wheel-type off-road vehicles. For a theoretical analysis of vehicle dynamics, it is a common practice to define the motion equations in reference to the body of the vehicle, and so vehicle-fixed coordinate systems are often used to describe the fundamental dynamics of vehicles [1]. As depicted in Figure 2.1, a conventional vehicle coordinate system consists of body-fixed coordinates (hereafter the body coordinates) and steering wheel-fixed coordinates (hereafter the wheel coordinates). The origin of body coordinates is often defined as the center of gravity (CG) of the vehicle, with its X CG direction pointing in the direction of travel (or longitudinal motion), its Y CG coordinate following the left-side direction (also denoted the lateral motion), and its Z CG direction indicating the vertical direction. The wheel coordinates, also represented in Figure 2.1, are defined with their origin at the center of the axle connecting both front wheels (sometimes referred to as the center of the axle, CA), its x st direction pointing in the forward longitudinal direction, and the y st and z st coordinates defined similarly to those of the body coordinates. The origin of the wheel coordinates is offset from that of the vehicle coordinates by a fixed distance determined by the physical separation of the vehicle’s center of mass (CG) from the axle center of the front (steered) wheels (CA).