Limitations and improvements in the idle speed control of a direct injection spark ignition engine.

One of the aims of automotive powertrain research is to balance the often-conflicting goals of performance; emissions control, and fuel economy. Among the outcomes of this research is the direct injection spark ignition (DISI) engine. This engine can operate in multiple modes, including a stratified charge mode with air-fuel ratio as large as 50:1. Operating in stratified mode results in improved fuel economy and reduced CO 2 emissions. The stratified charge mode is often employed during low speed and load conditions, such as during engine idle. This advanced technology engine has introduced a number of challenging control problems. The literature, however, does not contain a control-oriented model, complete with parameter values, for an engine of this type. We construct a generic, control-oriented model based on existing, published conventional engine models, and an assumption on the DISI indicated torque. Results using the model are compared to existing results in the literature. The idle speed control problem is considered next. This problem is cast as a two-input-two-output (TITO) control problem, and a control topology from the literature that partially decouples the coupled TITO plant is examined. We develop a baseline idle speed controller via decoupled loop closure. Significant delays, however; inhibit our ability to improve the transient response of the engine speed and in-cylinder air-fuel ratio via feedback alone. A multivariable scheme employing reference feedforward is proposed, and several potential topologies are presented. A reference feedforward algorithm is derived, and nonlinear simulation results are shown in which the speed and air-fuel ratio responses are improved considerably. The effectiveness of reference feedforward in improving the transient response can also be limited by delays. The delays are modeled as Pade approximations, and the effects due to the nonminimum phase zeros that are introduced are analyzed in the context of a Poisson integral constraint. Sensitivity and robustness issues of a decoupling control design are reviewed, and an analysis of stability robustness to air-fuel ratio transport delay and measurement dynamics is presented. Finally, further research directions are proposed.Ph.D.Applied SciencesElectrical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123272/2/3068957.pd