| abstract |
A variable-cycle engine operates in a two-cycle mode when the rotational speed of the engine is lower than a predetermined speed (N2) and in a four-cycle mode when the rotational speed of the engine is higher than the predetermined speed (N2). The engine has a first intake port and an exhaust port which are defined in an upper portion of a cylinder (1), and a second intake port (12) defined in a lower side portion of the cylinder. When the rotational speed of the engine is lower than the predetermined speed (N2), the engine operates as a two-cycle engine with the second intake valve (3) and the exhaust valve (17) in operation. When the rotational speed of the engine is higher than the predetermined speed (N2), the engine operates as a four-cycle engine with the first intake port and the exhaust port in operation. Alternatively, the engine has an intake port (130) defined in a lower side portion of a cylinder and an exhaust port defined in an upper portion of the cylinder, the exhaust port being openable and closable by an exhaust valve (240) with variable timing. Depending on the rotational speed of the engine, the timing with which the exhaust valve operates is varied, and the engine operates in one of different cycles. The engine is associated with a turbocharger (7) combined with an electric motor (72). In a lower speed range, the electric motor is energized to assist in turbocharging operation for thereby increasing the torque produced by the engine. |