Closed loop system

Abstract

A closed loop system for the control of the air/fuel ratio of an internal combustion engine is disclosed. The system includes an open loop air/fuel ratio controller that has a closed loop correction applied to its basic pulse width control signal. The closed loop correction is based upon the bi-level switching of an oxygen sensor detecting a substantially stoichiometric condition in the exhaust gas of the internal combustion engine. Performing the correction is an integral controller which responds to the switching of the exhaust gas sensor to increase the air/fuel ratio for one level of the sensor and to decrease the air/fuel ratio for the other level. The limit cycle oscillation developed by the integral controller is modified by increasing the authority and gain rate of the controller as a function of the distance the system is away from a reference point so that it responds to transient conditions rapidly and smoothly. Another aspect of the invention provides for the authority modification to take place when the controller reaches a threshold and to employ minimum constant authority for quiescent conditions. Also, in response to a closed throttle or idle condition the quiescent authority level is reduced to a convenient idle level to prevent torque roll.