Abstract: In a case where an internal combustion engine is executing an all-cylinder operation to operate all cylinders, an air-fuel ratio estimation part of an ECU 1 estimates an air-fuel ratio of each of the cylinders by using a first observer. On the other hand, in a case where the internal combustion engine is executing a cylinder-cut operation to rest a part of the cylinders and to operate other of the cylinders, the air-fuel ratio estimation part does not estimate the air-fuel ratio of each of the cylinders by using the first observer.

Abstract: A hybrid vehicle having a power-transferable combination of an engine and a motor-generator is controlled to prevent a vehicle vibration while preventing an over-revolution of the engine when the engine is started. In such control, while the engine is determined to be in a starting state, an instruction value correction is performed for correcting a per-unit-time change amount of an actuator instruction value, such as a target air intake amount and/or a target air load amount, according to a target output of the engine so that a steep increase of the engine revolution speed is prevented. With such a correction of the instruction value, an air intake amount of the engine and the engine revolution speed is gradually increased, thereby preventing the over-revolution of the engine and a steep increase of a load torque of the motor-generator, which prevents vehicle vibration when the engine is started.

Abstract: A hybrid vehicle having a power-transferable combination of an engine and a motor-generator is controlled to prevent a vehicle vibration while preventing an over-revolution of the engine when the engine is started. In such control, while the engine is determined to be in a starting state, an instruction value correction is performed for correcting a per-unit-time change amount of an actuator instruction value, such as a target air intake amount and/or a target air load amount, according to a target output of the engine so that a steep increase of the engine revolution speed is prevented. With such a correction of the instruction value, an air intake amount of the engine and the engine revolution speed is gradually increased, thereby preventing the over-revolution of the engine and a steep increase of a load torque of the motor-generator, which prevents vehicle vibration when the engine is started.