Control circuit for use with air-diverter valve of internal combustion

Abstract

An electronic control circuit for actuating a solenoid-operated air-diverter valve or valves connected with the exhaust manifold of an internal combustion engine, to supply supplemental air thereto. The supplemental air reacts with some of the hot exhaust gases, producing other gases which are in general less toxic than those coming directly from the engine. The circuit responds to engine speed in such a manner that, after a predetermined period of operation has elapsed during which the speed was continuously above a predetermined value, the normally energized solenoids are shut off to thus close the diverter valves and thereby interrupt the flow of supplemental air to the exhaust manifold. This prevents overheating of the exhaust system at high engine speeds. Provision is made for automatically modifying the operation of the circuit if the engine speed varies or fluctuates between relatively high and low speeds, and circuit operation is dependent on the relative time intervals involved with each type of operation. Self-diagnostic controls are also included, in order to assist the vehicle operator in determining that the circuit is functioning properly. The arrangement is such that the air-diverter valves are open most of the time, in order to minimize overall exhaust pollutants, but close when necessary in order to prevent excessive heat in the exhaust system from being developed.