Stephen William Magner

Variable cam timing: Consequences to automotive engine control design

Abstract One objective of this paper is to illuminate fuel economy and emission improvement mechanisms of variable cam timing systems and analyze their effects on engine control system design. By retarding or advancing the cam phase one can vary the engine volumetric efficiency, as well as the amount of exhaust gas that dilutes the air charge. Combining these effects with intake manifold and engine speed dynamics leads to a complex behavior of engine air-charge and torque that requires special handling by the engine control system. This paper reviews control algorithms for VCT engines that have been reported in the literature.

Disturbance attenuation in time-delay systems — A case study on engine air-fuel ratio control

In this paper we analyze relative performance of several approaches to disturbance attenuation for systems with time delay including the conventional Proportional-Integral controller, the Smith Predictor, and the Model Reduction controller. The paper proposes a measure of disturbance attenuation capability and computes it analytically for each of the controllers considered. The results are applied to the air-fuel ratio regulation in automotive engines. To meet strict emission regulations, gasoline engines must operate at stoichiometric air fuel ratio over most of its operating range. A major component towards accomplishing this goal is the closed loop fuel controller. The feedback uses an exhaust-gas oxygen sensor which introduces a long transport delay. This paper discusses the air-fuel ratio regulation problem, explores options in control design for disturbance attenuation in system with time-delay, and shows simulation and experimental, in-vehicle validations.

Fuel economy optimization in automotive engines

Automakers have introduced a number of devices, such as the exhaust gas recirculation valve and variable cam timing (VCT), intended to vary with operating conditions previously fixed by engine design. Scheduling set points for these devices and adjusting dependent parameters, such as spark advance, to optimize fuel economy and emissions typically require extensive engine dynamometer mapping. Exhaustively mapping all feasible combinations is prohibitive. Design of Experiments (DOE) has greatly reduced conventional engines mapping time and will be required for more complex engine configurations. On the other hand, caution must be exercised in applying DOE methods if the full benefit of new actuators is to be realized. This paper examines potential fuel economy losses directly attributable to steady state engine characterization by using a dual-independent VCT engine as the platform

Delta air-charge anticipation for mass air flow and electronic throttle control based systems

Cylinder air charge estimators, that account for the air flow dynamics of the engine, are an essential feature to engine emission control systems. These estimators must be further augmented to anticipate the air charge several cylinder events beyond the current estimate due to practical fuel injector limitations. The delay between the commanded and measured throttle position of an electronic throttle controller (ETC) can be used to improve the air charge anticipation algorithms. We develop an air charge algorithm that exploits a one cylinder event ahead prediction of the throttle position to determine air charge one or two cylinder events in the future. We explore a practical method of obtaining the prediction of throttle using an ETC as well as more sophisticated methods to determine the extent of throttle prediction accuracy that is possible over a range of prediction times.

Multi-input transient fuel control with auto-calibration

Most engine transient fuel control methods use the mass of injected fuel to drive the compensator dynamics. This works well in conventional engines because several other main factors that affect the fuel puddle, such as mass air-flow and manifold air pressure (MAP), are coupled closely with the injected fuel. In variable cam timing (VCT) engines, MAP and mass of injected fuel are decoupled to the point that they may move in opposite directions under certain conditions. To circumvent this problem we propose using MAP as the second input to compensate for fuel puddle dynamics. The structure of the new compensator is derived from a detailed model of the puddle dynamics. Further, we provide a method to automatically fit the new model and compensator parameters from dynamometer data. The model and compensator performance is illustrated by simulations and experiments.

Influence of Intake Manifold Heat Transfer Effects on Accuracy of SI Engine Air-Charge Prediction

Estimation of the actual cylinder air charge and air-charge prediction several engine events into the future are needed to implement an air-fuel ratio feedforward controller. The estimator/predictor is usually based on the isothermal intake manifold model which assumes constant temperature of manifold air. However, fast thermocouple measurements have pointed to significant changes of manifold air temperature during typical tip-in/tip-out engine transients. In order to capture the temperature change effect, the manifold dynamics should be described by the so-called polytropic model. This paper presents an algebraic and simulation analyses of the influence of manifold modeling errors on the accuracy of air-charge prediction. The analysis is conducted for a typical predictor given in two variants depending on whether the throttle mass flow sensor or the manifold pressure sensor is used.Copyright

Control of engines with fully variable valvetrains

To improve performance, fuel economy, and emissions of automotive engines, automakers have introduced a number of devices intended to vary a previously fixed engine parameter with operating condition. Such devices include variable cam timing and valve lift, variable compression ratio, intake manifold tuning, etc. Combining these devices in an engine promises improved fuel economy, but raises the issue of scheduling and coordination to achieve the benefit and prevent undesirable failure modes. This paper introduces the problem of controlling a fully variable valvetrain configuration, and shows an algorithm for synchronizing variables that have different rates of response with the goal of preventing potential piston-valve interference in mechanically unprotected engines.