Abstract: An integrated control device has a plurality of exhaust gas control units and base board means for mounting the control units thereon. The base board means is provided with fluid passage means and port opening means communicating therewith and adapted to be mated with port means in the control units so as to establish necessary fluid communication among the control units. Thus, the arrangement of the components used in an exhaust gas cleaning system can be made compact and readily accessible.

Abstract: Disclosed herein is a comparator circuit used in a system for controlling, in accordance with an air-fuel ratio signal from an O.sub.2 sensor arranged in an exhaust system of an internal combustion engine, the air-fuel ratio of the exhaust gas. The comparator has two inputs, one of which receives a signal having a phase which is the same as a signal from the O.sub.2 sensor, the other of which receives a delayed phase signal. The output of the comparator operates to provide, in accordance with the voltage level difference between the inputs, two deviation signals, one of which indicates that air-fuel ratio has deviated to the rich side of the air-fuel ratio the other of which indicates that the air-fuel ratio has deviated to the lean side of the air-fuel ratio.

Abstract: An apparatus is provided for introducing secondary air for into an internal combustion engine. The apparatus has an air pump coupled to an air injection pipe system, the latter having an end terminating upstream of the catalytic converter, for introducing an amount of secondary air into the exhaust system of the engine. The apparatus further includes a valve device for maintaining the secondary air directed to the exhaust system from the air pump at determined constant pressure; thus, the amount of secondary air introduced into the exhaust system is effectively decreased during high rotational speed engine operation in order to prevent the catalytic converter from being overheated.

Abstract: A thermostatic valve, used in an engine for introducing warmed air to the engine and air to a slow-port passage of a carburetor, has a valve casing defining therein first and second compartments. A first valve member is disposed in the first compartment to control the introduction of the intake vacuum or the atmospheric pressure to a negative pressure motor mounted on a throat of an air cleaner. A second valve member is disposed in the second compartment to control the communication between a float chamber and the slow-port passage of the carburetor when the temperature of the air introduced into the engine exceeds a preset value so as to prevent excessive richness of an air-fuel mixture.