Control Method for Hybrid Vehicle and Control System for Hybrid Vehicle

A control system for a hybrid vehicle, comprising:

• a drive motor;
• a battery configured to exchange electric power with the drive motor;
• a generator driven by an engine for power generation and configured to generate power in response to a power generation request for driving associated with a driver operation to charge the battery;
• a catalyst for treating exhaust gas discharged from the engine;
• and
• a control unit configured to control the battery, the engine, and the generator, wherein available input electric power to the battery is set to be lower as a state of charge of the battery approaches a predetermined upper limit value, and the control unit is configured to:
• stop a fuel supply to the engine in a case where a temperature of the catalyst is equal to or lower than a predetermined temperature for suppressing deterioration of the catalyst at a time of stopping the power generation request for driving,
• start a power generation request for catalyst in a case where the temperature of the catalyst exceeds the predetermined temperature at the time of stopping the power generation request for driving,
• drive the engine at a best fuel efficiency operating point at which an output efficiency of the engine is maximized in a coordinate space having a rotation speed and a torque of the engine as axes at the time of stopping the power generation request for driving, and drive the engine at the best fuel efficiency operating point at the time of starting the power generation request for catalyst,
• move, in a case where the available input electric power is lower than electric power obtained by driving the engine at the best fuel efficiency operating point, an operating point from the best fuel efficiency operating point to a location where the rotation speed becomes a predetermined lower limit rotation speed along an efficient operating line that includes the best fuel efficiency operating point in the coordinate space and that is represented as a trace of an efficient operating point at which fuel efficiency of the engine is minimized when the engine is driven at the operating point having a lower output than that of the best fuel efficiency operating point, and
• then reduce the torque in a state in which the rotation speed is maintained at the predetermined lower limit rotation speed when the available input electric power is further reduced.