Gm Global Technolgoy Operations, Inc.

John F Schweikert

Alan F Chiesa

LeRoy E Medendorp

Edward E Durham

Edward C Perry

David S Grossman

A system is described for diagnosing the operation of an exhaust gas recirculation system of an internal combustion engine having a speed density fuel delivery system and having a closed loop fuel adjustment. The EGR system operation is determined by disabling the EGR system and observing the magnitude of change of the integral adjustment of the closed loop system.

EGR diagnostic system

A spark timing control system for an internal combustion engine is responsive to a changing engine operating parameter signalling an engine tip-in event to retard spark timing by an amount sufficient to eliminate tip-in knock and for a predetermined time period ending 175-300 milliseconds after initiation of the tip-in event, so that no perceptible engine performance loss results.

Tip-in knock eliminating spark timing control

A closed loop air/fuel ratio controller for an internal combustion engine includes a control circuit responsive to the output of an exhaust gas sensor representing at least the sense of deviation of the air/fuel ratio of the mixture supplied to the engine from stoichiometry and provides a control signal which is used to adjust the air/fuel ratio of the mixture supplied to the engine in direction tending to restore a stoichiometric air/fuel ratio. The control signal includes an integral correction term and an asymmetrical proportional correction term that abruptly shifts the value of the control signal upon a detected change in at least one direction in the sense of the deviation of the air/fuel ratio from a stoichiometric air/fuel ratio. The asymmetrical proportional term provides either singularly or in combination with an asymmetrical integral term a scheduled air/fuel ratio offset from the stoichiometric air/fuel ratio with the offset value being a function of the system gains and the limit cycle frequency of the control signal that is determined primarily by the transport delay through the engine and exhaust system.

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Sterling Heights, MI, United States of America

John F Schweikert