Vehicle Controls

Vehicle control systems typically include chassis components that influence vehicle dynamics in three directions: longitudinal, lateral, and vertical. These three degrees of freedoms are controlled by chassis actuators such as brakes, steering, and suspensions, respectively. Traditionally, they were all mechanically controlled. For example, steering was actuated by the driver turning a steering wheel, which then caused the hydraulics in a power steering unit to amplify the driver-imposed torque and to create a desired wheel/tire rotation at the point of contact with the road. During the past couple of decades, the above mechanical actuations have gradually been augmented by electrical and electronics/mechatronics actuations. This created opportunities for applications of computer controls and associated software. The early computer controls applications started with relatively slow (low bandwidth) load leveling suspensions and antilock braking systems (ABS). Later these were augmented by active and semiactive suspensions and four-wheel steer vehicle controls. On the other hand, there was development in traction controls for improved performance and stable operations on various road surfaces. This was further extended toward full vehicle stability control where brake intervention on one side of the vehicle was introduced in order to improve yaw stability and controllability. Additional enhancement was made possible by roll stability control (RSC) to further improve stability in the roll direction and mitigate possible degraded performance. This chapter addresses various aspects of vehicle control systems, starting from modeling of vehicle dynamics and associated tire characteristics, to active suspension and vehicle stability controls, concluding with active steering control and related future advanced control applications.