Abstract: A lean burn engine adapted to establish a specified air-fuel ratio leaner by predetermined rate than a stoichiometric air-fuel ratio in a range of low engine speeds and low engine loads is provided with an air intake system of a low speed type which provides a high charging efficiency in a range of low engine speeds and an exhaust system capable of eliminating a nitrogen oxide emission in the exhaust even during lean burning.

Abstract: A knock control system for a supercharged engine comprising a supercharger for providing a super charged air to the engine, an engine condition detector for detecting an engine operating condition, a knock detector for detecting the occurrence of engine knocking, an ignition timing determining unit, a supercharged pressure regulator, an ignition timing correcting unit, and a supercharged pressure correcting unit. The timing determining unit is operable to determine a principle ignition timing in response to an output from the condition detector, and the timing correcting unit is operable in response to an output from the knock detector to adjust the principle ignition timing in the event of occurrence of the knocking.

Abstract: An engine intake system includes a combustion chamber, a first intake port opening to the combustion chamber, and a second intake port opening to the combustion chamber. A shut-off valve is provided for blocking intake gas flow to the combustion chamber through the second intake port in a first engine operating region wherein engine load is relatively small, and allowing the intake gas to flow to the combustion chamber through the second intake port in a second engine operating region wherein the engine load is relatively large. A first valve actuating mechanism is provided for opening the first intake valve at a first timing, and a second valve actuating mechanism is provided for opening the second intake valve at a second timing.

Abstract: An internal combustion engine has an air-fuel ratio control system, an exhaust gas recirculation system and an ignition system. At least one of the systems is adjusted when the intake air temperature is very high so that fast combustion is suppressed. The adjustment is effective to prevent detonation or similar unusual combustion which may occur under a very high temperature of the intake air.

Abstract: An engine exhaust gas recirculation system including a recirculation gas control valve provided in a gas recirculation passage. The gas recirculation passage is further provided with a restriction and pressure sensors for detecting the pressure drop across the restriction so that the opening of the control valve be adjusted in accordance with the engine operating conditions and with a prestored memories of optimum values of the pressure drop. The restriction is variable so that the effective opening thereof is increased as the recirculated gas flow increases.