Abstract: A control device controls a valve timing changer to retard a phase of an exhaust valve camshaft with respect to a crankshaft such that the time of opening of an intake valve is earlier than the time of closing the exhaust valve after a top dead center, when a determiner determines that an engine is not in a warm-up stage in a low-load operation. The control device controls the valve timing changer to advance the phase of the exhaust valve camshaft with respect to the crankshaft such that the time of closing the exhaust valve is earlier than the time of opening of the intake valve after the top dead center, when the determiner determines that the engine is at the warm-up stage in the low-load operation.

Abstract: A control device controls a valve timing changer to retard a phase of an exhaust valve camshaft with respect to a crankshaft such that the time of opening of an intake valve is earlier than the time of closing the exhaust valve after a top dead center, when a determiner determines that an engine is not in a warm-up stage in a low-load operation. The control device controls the valve timing changer to advance the phase of the exhaust valve camshaft with respect to the crankshaft such that the time of closing the exhaust valve is earlier than the time of opening of the intake valve after the top dead center, when the determiner determines that the engine is at the warm-up stage in the low-load operation.

Abstract: A four-cycle engine (1) structured to introduce fresh air into a cylinder (1a) via an intake port (1d) opened/closed by intake valves (IN1, IN2) and suck exhaust gas back into the cylinder (1a) via an exhaust port opened/closed by exhaust valves (EX1, EX2), wherein the exhaust port has a first exhaust port (1p) and a second exhaust port (1e), and the exhaust gas is sucked in back from the first exhaust port (1p) and secondary air is sucked in from the second exhaust port (1e) to form, in the cylinder (1a), a first temperature layer (T1) at a high temperature mainly composed of the exhaust gas and a second temperature layer (T2) at a temperature lower than that of the first temperature layer (T1) mainly composed of the secondary air.