On the design of a vehicle longitudinal controller

A methodology for designing an automated vehicle longitudinal controller is presented and applied to an automobile characterized by velocity-dependent dynamics. The design consists of a cascade compensator, which is selected to achieve small tracking errors, and an observer/controller compensator. The controller portion was designed to achieve a velocity-invariant response, and the observer to derive the state-feedback signals. Both compensators were realized on an eight-bit microcomputer, and the vehicle dynamics were simulated on an analog computer. The performance of the resulting system was evaluated using a large-signal, entry merging command and small-signal mainline commands. Excellent results were obtained with typical values being a maximum position error of 0.63 m during an entry maneuver and 0.15 m during a mainline maneuver; however, the designed system was sensitive to large changes in critical vehicle parameters. Thus, there is a need to modify the controller so that it can adaptively compensate for such changes. Then, the designed digital controller, with its flexibility to perform other functions and its ease of reliability enhancement, is an attractive candidate for implementation, and at the very least, indicates the type of longitudinal performance one can expect from a realistically designed controller over the speed range 0-30 m/s.