M.-S. S. Ashhab A. G. Stefanopoulou e-mail: anna@engineering.ucsb.edu Mechanical and Environmental Engineering Department, University of California, Santa Barbara, CA 93106 J. A. Cook M. B. Levin Ford Motor Company, Scientific Research Laboratory, Dearborn, MI 48121 Control-Oriented Model for Camless Intake Process—Part I 1 The improvement of internal combustion engine is largely accomplished though the in- troduction of innovative actuators that allow optimization and control of the flow, mixing, and combustion processes. The realization of such a novel system depends on the exis- tence of an operational controller that will stabilize the engine and allow experimental testing which, consequently, leads to further development of the actuator and the engine controller. This iterative process requires a starting point which is the development of a control-oriented model. Although not fully validated, the control-oriented model reveals issues associated with uncertainties, nonlinearities, and limitation of different subsystems. Moreover, it aides in defining the controller structure and the necessary parameters for the calibration of the closed loop system. In this paper (Part I) we describe the develop- ment process of a control-oriented model for a camless intake process. We first model the multicylinder crankangle-based breathing dynamics and validate it against experimental data of a conventional engine with cam-driven valve profile during unthrottled operation. We then employ the assumption of uniform air pulses during the intake duration and derive a simple input-output representation of the cylinder air charge, pumping losses and associated uncertainties that can be used for designing an electronic valvetrain controller (Part II). S0022-04340002901-4 1 Introduction Various analytical and experimental studies of engines equipped with innovative valvetrain mechanisms have shown that controlling cylinder air charge with the intake valve motion can reduce pumping losses and thus increase fuel economy Elrod and Nelson 1, Gray 2 1988, Ma 3. This is achieved by eliminat- ing the need to throttle the air flow into the intake manifold which is the traditional means of controlling the engine load in spark ignition engines. By using electronically controlled intake val- vetrain developed in Schechter and Levin 4, one can eliminate the main throttle body and directly regulate the air flow into the cylinders. We refer to this engine conditions as unthrottled opera- tion. Control of unthrottled variable valve motion if combined with other currently pursued technologies, namely, lean combus- tion and/or engines with high level of dilution Meacham 5, can alleviate current compromises between idle stability, fuel economy, and maximum torque performance. An automatic controller is necessary to regulate the additional degrees of freedom of camless engine operation, namely, valve lift and opening-closing timing. Developing such a controller re- quires knowledge of how, at least qualitatively, the additional de- grees of freedom affect the engine intake process. It is thus nec- essary to develop an engine model for control development even though experimental data of the actual system are not available. In this paper, we concentrate in capturing the dominant dynamic behavior of the intake process and investigating the sensitivity of the model to higher order dynamics that are, in general, uncertain or difficult to model. In contrast to the mathematical models de- veloped for subsystem optimization, our goal is to reveal potential difficulties in the control design due to subsystem limitations, nonlinearities, and uncertainty. We first develop a phenomeno- logical multicylinder and crankangle based model of the intake process. The crankangle based model consists of dynamical equa- tions using first principles and engine/actuator geometrical char- acteristics and static empirical relations based on data and is validated against experimental data of a conventional engine with cam-driven valve profile during unthrottled operation. We then derive the control-oriented model for the cylinder air charge and the pumping losses assuming uniform air pulses during the intake duration. We show that this assumption leads to a simple input- output representation that can be used for the development of a cylinder air charge controller and for the minimization of pump- ing losses. We finally, investigate the modeling uncertainty due to often unknown higher order dynamics. This paper is intended to fill the gap between the work on camless actuation design, and the work related to steady-state engine optimization. Work in the area of actuator design can be found in Gray 2, Moriya et al. 6, Schechter and Levin 4 and references therein. Only a few papers in this category address issues associated with closed-loop actuator operation and performance that enable steady-state engine operation. The most comprehensive study of the inner loop controller for a camless valvetrain actuator can be found in Anderson et al. 7. The authors develop and test an adaptive algorithm for maximum lift control that enables stable actuator operation for the electro-hydraulic camless valvetrain de- veloped in Schechter and Levin 4 and modeled in Kim et al. 8. Engine optimization studies and sensitivity analysis can be found in Gray 2, Ahmad and Theobald 9, Sono and Umiyama 10, and Ashhab et al. 11. Finally, studies on the feedback controller design and the engine management system are scarce Urata et al. 12, Ashhab et al. 11. In Urata et al. 12 the authors tune a proportional-derivative idle speed controller. They also design an air-to-fuel ratio A/F feedback loop by using oxygen sensor in the exhaust of each cylinder and correct individual cylinder intake valve timing. A more attractive solution of balancing A/F mald- istributions is demonstrated in Moraal et al. 13 where a single manifold pressure sensor is used to estimate conventional val- vetrain component variability and then adjust fuel pulsewidth du- ration of individual cylinders. In all the previous work neither unthrottled nor camless operation was considered and the results are restricted to a 4-cylinder case. This paper is organized as follows. We describe the crankangle- based phenomenological engine model with the camless actuator in Section 2. Section 4 includes validation results. The control- oriented model is then derived in Section 5 and in Section 6 we calculate uncertainty models for control development. It is shown 1 Research supported in part by the National Science Foundation under contract NSF ECS-97-33293 and the Department of Energy Cooperative Agreement No. DE- FC02-98EE50540; matching funds were provided by Ford Motor Co. Contributed by the Dynamic Systems and Control Division for publication in the JOURNAL OF DYNAMIC SYSTEMS,MEASUREMENT, AND CONTROL. Manuscript received by the Dynamic Systems and Control Division July 14, 1998. Associate Technical Editor: G. Riggoni. 122 Õ Vol. 122, MARCH 2000 Copyright © 2000 by ASME Transactions of the ASME