Vehicle Dynamics and Control

Chapter 4 LONGITUDINAL VEHICLE DYNAMICS (p. 95)

The control of longitudinal vehicle motion has been pursued at many different levels by researchers and automotive manufacturers. Common systems involving longitudinal control available on today's passenger cars include cruise control, anti-lock brake systems and traction control systems. Other advanced longitudinal control systems that have been the topic of intense research include radar-based collision avoidance systems, adaptive cruise control systems, individual wheel torque control with active differentials and longitudinal control systems for the operation of vehicles in platoons on automated highway systems.

This chapter presents dynamic models for the longitudinal motion of the vehicle. The two major elements of the longitudinal vehicle model are the vehicle dynamics and the powertrain dynamics. The vehicle dynamics are influenced by longitudinal tire forces, aerodynamic drag forces, rolling resistance forces and gravitational forces. Models for these forces are discussed in section 4.1. The longitudinal powertrain system of the vehicle consists of the internal combustion engine, the torque converter, the transmission and the wheels. Models for these components are discussed in section 4.2.

4.1 LONGITUDINAL VEHICLE DYNAMICS
Consider a vehicle moving on an inclined road as shown in Figure 4-1. The external longitudinal forces acting on the vehicle include aerodynamic drag forces, gravitational forces, longitudinal tire forces and rolling resistance forces. These forces are described in detail in the sub-sections that follow.