Seibum B. Choi

Direct adaptive longitudinal control of vehicle platoons

An important aspect of an automated highway system design is the synthesis of an automatic vehicle following system. Associated with automatic vehicle following systems is the problem of the stability of a string of vehicles, i.e., the problem of spacing error propagation, and in some cases, amplification upstream from one vehicle to another, due to some disturbance at the head of the string. Realistic vehicle following designs must also address parametric uncertainties such as mass of the vehicle, aerodynamic drag, and tire drag. The mass of the vehicle varies with the number of passengers. At small intervehicular separations, aerodynamic drag force changes significantly with the distance to be maintained. We address the problem of stability of a vehicle string in the presence of parametric uncertainty and present a Lyapunov-based decentralized adaptive control algorithm to compensate for such parametric variations. We examine this direct adaptive control algorithm for platoon performance and parameter convergence. We present the simulation results to demonstrate the effectiveness of the adaptive controller.

An observer-based controller design method for improving air/fuel characteristics of spark ignition engines

The wide operating range, the inherent nonlinearities of the induction process and the large modeling uncertainties make the design of the fuel-injection controller very difficult. Even though a sliding mode fuel-injection control method is in good agreement with the characteristics of the system, the unavoidable large time-delay between control action and measurement causes the problem of chattering. In this paper, an observer-based fuel-injection control algorithm is suggested for fast response and small amplitude chattering of the air-to-fuel ratio. The characteristics of the proposed controller are compared with those of other controllers. The proposed controller is simple enough for online computation and is implemented on an automotive engine using a PC-386. The simulation and the experimental results show that this algorithm reduces the chattering magnitude considerably while speeding up the transient response and is robust to modeling errors.

Robust Throttle Control of Automotive Engines: Theory and Experiment

An adaptive, sliding control algorithm is developed for automated throttle control of an I.C. engine to be used in drive-by-wire applications such as coordinated engine/transmission gear shiftings, traction control and autonomous vehicle control (IVHS). The paper presents a new sliding control formulation that includes combustion transport delays and a simplified adapation law to account for slowly varying engine parameters. The new technique is evaluated by computer simulation and laboratory dynamometer tests.

Air-to-fuel ratio control of spark ignition engines using Gaussian network sliding control

This paper treats air-to-fuel ratio control of a spark ignition engine. A direct adaptive control method using Gaussian neural networks is developed to compensate transient fueling dynamics and the measurement bias of mass air flow rate into the manifold. The transient fueling compensation method is coupled with a dynamic sliding mode control technique that governs fueling rate when the throttle change is not rapid. The proposed controller is simple enough for online computation and is successfully implemented on an automotive engine having a multiport fuel injection system.

Vehicle longitudinal control using an adaptive observer for automated highway systems

This paper summarizes data fusion, controller design and experimental work done recently for the longitudinal control of a platoon of autonomous vehicles. This paper presents alternative sub-models of an engine and a transmission to achieve the goal of precise spacing control with smooth ride quality. Adaptive observers are developed to estimate the vehicle-to-vehicle spacing and the closing rate. The estimated values are used in a sliding mode based controller. The developed control strategies are implemented on test vehicles and four vehicle platoon control performed at low to highway speed profiles using throttle position control alone.

Antilock Brake System With a Continuous Wheel Slip Control to Maximize the Braking Performance and the Ride Quality

In this paper, a new type of antilock brake system (ABS) algorithm is developed. A full-time feedback control algorithm differentiates the new ABS from rule-based conventional ABS algorithms. The rear wheels are controlled to create limit cycles around the peak friction slip points. From the cycling patterns of the rear wheels, the optimal slips are defined. The front wheels are controlled to track the optimal slips defined by monitoring the behaviors of the rear wheels. The new algorithm can be implemented on any production ABS hardware without any modification or extra sensors. The test results show significant performance improvement in both the stopping distance and the noise, vibration, and harshness on homogeneous surfaces, and also quick detection of surface transition. The robustness of the new ABS algorithm is proven by vehicle tests on various speeds, surfaces, and driving conditions.

Unified Chassis Control for the Improvement of Agility, Maneuverability, and Lateral Stability

This paper describes a unified chassis control (UCC) strategy for improving agility, maneuverability, and vehicle lateral stability by the integration of active front steering (AFS) and electronic stability control (ESC). The proposed UCC system consists of a supervisor, a control algorithm, and a coordinator. The supervisor determines the target yaw rate and velocity based on control modes that consist of no-control, agility-control, maneuverability-control, and lateral-stability-control modes. These control modes can be determined using indices that are dimensionless numbers to monitor a current driving situation. To achieve the target yaw rate and velocity, the control algorithm determines the desired yaw moment and longitudinal force, respectively. The desired yaw moment and longitudinal force can be generated by the coordination of the AFS and ESC systems. To consider a performance limit of the ESC system and tires, the coordination is designed using the Karush-Kuhn-Tucker (KKT) condition in an optimal manner. Closed-loop simulations with a driver-vehicle-controller system were conducted to investigate the performance of the proposed control strategy using the CarSim vehicle dynamics software and the UCC controller, which was coded using MATLAB/Simulink. Based on our simulation results, we show that the proposed UCC control algorithm improves vehicle motion with respect to agility, maneuverability, and lateral stability, compared with conventional ESC.

Design and Experimental Implementation of Longitudinal Control for a Platoon of Automated Vehicles

This paper presents the design and experimental implementation of a longitudinal control system for the operation of automated vehicles in platoons. The control system on each vehicle is designed to have a hierarchical structure and consists of an upper level controller and a lower level controller. The upper controller determines the desired acceleration for each vehicle in the platoon so as to maintain safe string-stable operation even at very small intervehicle spacing. The lower controller utilizes vehicle-specific parameters and determines the throttle and/or brake commands required to track the desired acceleration. A special challenge handled in the design of the lower level controller is low-speed operation that involves gear changes and torque converter dynamics. The paper also presents the design of longitudinal intra-platoon maneuvers that are required in order to allow any car in the platoon to make an exit. The paper presents extensive experimental results from the public NAHSC demonstration of automated highways conducted in August 1997 at San Diego, California. The demonstration included an eight-car platoon operating continuously over several weeks with passenger rides given to over a thousand visitors. The maneuvers demonstrated included starting the automated vehicles from complete rest, accelerating to cruising speed, allowing any vehicle to exit from the platoon, allowing new vehicles to join the platoon and bringing the platoon to a complete stop at the end of the highway.@S0022-0434~00!01903-1#

Design and Modeling of a Clutch Actuator System With Self-Energizing Mechanism

The engineering technology for automotive systems is currently edging toward improving fuel economy. Transmission is one of the major parts to determine overall energy efficiency. The goal of this paper is to investigate the feasibility of a new clutch actuator in order to increase power transmitting efficiency. The new clutch actuator has self-energizing mechanism to amplify the normal force applied on the contact surfaces for the engagement. It allows the clutch module to consume less amount of energy for actuating the overall system. The equations of motion of the clutch mechanism coupled with a dc motor are represented to capture the essential dynamics. By using the proposed model, a model-based position-tracking controller is developed for the engagement of the clutch. Also, passivity analysis of the actuator system is performed to prevent the clutch from being stuck. Finally, the self-energizing effect and torque transmissibility of the proposed system and motion controller are validated experimentally.

Linearized Recursive Least Squares Methods for Real-Time Identification of Tire–Road Friction Coefficient

The tire-road friction coefficient is critical information for conventional vehicle safety control systems. Most previous studies on tire-road friction estimation have only considered either longitudinal or lateral vehicle dynamics, which tends to cause significant underestimation of the actual tire-road friction coefficient. In this paper, the parameters, including the tire-road friction coefficient, of the combined longitudinal and lateral brushed tire model are identified by linearized recursive least squares (LRLS) methods, which efficiently utilize measurements related to both vehicle lateral and longitudinal dynamics in real time. The simulation study indicates that by using the estimated vehicle states and the tire forces of the four wheels, the suggested algorithm not only quickly identifies the tire-road friction coefficient with great accuracy and robustness before tires reach their frictional limits but successfully estimates the two different tire-road friction coefficients of the two sides of a vehicle on a split- μ surface as well. The developed algorithm was verified through vehicle dynamics software Carsim and MATLAB/Simulink.