ENGINE ASSISTANCE CONTROL DEVICE AND ENGINE ASSISTANCE CONTROL METHOD

PROBLEM TO BE SOLVED: To more rationally assist engine output while recovering deceleration energy of a vehicle without waste.SOLUTION: An engine assistance control system includes: a motor generator 20; a capacitor 24 that stores electric power generated by the motor generator 20 and feeds electric power to the motor generator upon assisting engine output, a capacitor voltage sensor 31; and an ECU 30 that controls an engine 10 and the motor generator 20. If the electric power of the capacitor 24 is equal to or larger than a voltage value V1 close to a maximum value V, the ECU 30 implements active assistance control for assisting engine output over all operation domains. If the electric power falls below the voltage value V1, the ECU 30 implements optimal assistance control for assisting engine output using the motor generator over only a domain of higher loads than an engine torque (operation load) that brings the specific fuel consumption of the engine to a minimum value.