Exhaust emission control system in engine

Abstract

Selectively operable first and second exhaust valves are provided for every combustion chamber in an engine. Branch pipes of a first intake manifold are connected to first exhaust ports opened and closed by the first exhaust valves, and branch pipes of a second exhaust manifold are connected to second exhaust ports opened and closed by the second exhaust valves. An adsorbing trap is provided in an aggregated pipe of the first exhaust manifold and a catalytic converter is provided in a common exhaust pipe connected to the aggregated pipes of the first and second exhaust manifolds. Only the first exhaust valves are operated to open and close at a low temperature of the adsorbing trap to permit the exhaust gas to flow into the first exhaust manifold. Thus, hydrocarbons (HCs) in the exhaust gas are adsorbed into the adsorbing trap at the low temperature and the heat of the exhaust gas is effectively utilized to promote the activation of the catalytic converter. As the temperature increases sufficiently to activate the catalytic converter, the HCs adsorbed by the adsorbing trap are desorbed, which restores the HCs adsorbing capability of the adsorbing trap, and the exhaust gases are treated directly by the catalytic converted by operating the second exhaust valves while resting the first exhaust valves.