Closed-loop engine control: Analog or digital circuits to aid emissions control may be the forerunner of onboard engine “tuning”

To meet current US emission standards for automobiles, hydrocarbon (HC) and carbon monoxide (CO) emissions are usually controlled by a catalytic converter in the automobile exhaust. Federal standards for nitrogen oxides (NO_x) emissions are met mainly by exhaust-gas recirculation (EGR) techniques. However, in 1981, when NO_x emissions standards are tightened from the current limit of 2.0 grams per mile to 1.0 gram per mile, these techniques alone may no longer be sufficient. Although many schemes are under investigation for meeting the 1981 emissions standards for all three emissions, one of the most promising employs a three-way catalyst-for HC, CO, and NO_x emissions-in conjunction with a closed loop engine-control system. The problems involved in this approach and the engineering designs to solve these problems are addressed in this article.