Control method of air fuel ratio for hybrid vehicle and control device of air fuel ratio for hybrid vehicle
A control method for a hybrid vehicle configured to switch between stoichiometric combustion and lean combustion in which the target air fuel ratio is set to be leaner than the theoretical air fuel ratio is provided. The control method for the hybrid vehicle includes when the combustion mode is switched from the lean combustion to the stoichiometric combustion, stopping a fuel supply to the internal combustion engine; decreasing an intake air amount of the internal combustion engine during the stop; setting the target air fuel ratio of the internal combustion engine to the theoretical air fuel ratio, or the air fuel ratio richer than the theoretical air fuel ratio, in a state in which the intake air amount of the internal combustion engine is decreased; and restarting the internal combustion engine.
1 . A control method for a hybrid vehicle including a first motor configured to supply a generated electric power to a battery, a second motor configured to drive a driving wheel by the electric power from the battery, or the electric power generated by the first motor, and an internal combustion engine configured to drive the first motor, the hybrid vehicle being configured to switch between a stoichiometric combustion in which a target air fuel ratio of the internal combustion engine is set to a theoretical air fuel ratio, and a lean combustion in which the target air fuel ratio is set to be leaner than the theoretical air fuel ratio, the control method for the hybrid vehicle comprising:
when a combustion mode is switched from the lean combustion to the stoichiometric combustion,
stopping a fuel supply to the internal combustion engine;
decreasing an intake air amount of the internal combustion engine during the stop;
setting the target air fuel ratio of the internal combustion engine to the theoretical air fuel ratio, or the air fuel ratio richer than the theoretical air fuel ratio, in a state in which the intake air amount of the internal combustion engine is decreased; and
restarting the internal combustion engine,
wherein when a request torque of the internal combustion engine is greater than a predetermined value, in a case in which the combustion mode of the internal combustion engine is switched from the lean combustion to the stoichiometric combustion, the air fuel ratio is switched with the fuel supply continued.
2 . The control method for the hybrid vehicle as claimed in claim 1 , wherein when the combustion mode is switched from the lean combustion to the stoichiometric combustion, a rotation of the internal combustion engine is stopped, and the air fuel ratio is switched to the theoretical air fuel ratio, or the air fuel ratio richer than the theoretical air fuel ratio at the restart of the internal combustion engine.
3 . The control method for the hybrid vehicle as claimed in claim 2 , wherein the hybrid vehicle comprises an NOx trap configured to collect NOx in an exhaust gas;
when the NOx amount collected by the NOx trap catalyst becomes equal to or greater than a predetermined first threshold value, the combustion mode is switched from the lean combustion to the stoichiometric combustion; and
when the NOx amount collected by the NOx trap catalyst becomes smaller than the first threshold value, and equal to or greater than a predetermined second threshold value smaller than the first threshold value, the combustion mode is switched from the lean combustion to the stoichiometric combustion after a satisfaction of a predetermined switching request.
4 . The control method for the hybrid vehicle as claimed in claim 3 , wherein when the NOx amount collected by the NOx trap catalyst is smaller than the first threshold value, and equal to or greater than the second threshold value, in a case in which the internal combustion engine is stopped by a satisfaction of a predetermined internal combustion stop condition, the internal combustion engine is restarted after waiting for a satisfaction of a predetermined internal combustion engine start condition.
5 . The control method for the hybrid vehicle as claimed in claim 2 , wherein when the combustion mode is switched from the lean combustion to the stoichiometric combustion, an opening degree of a throttle valve configured to control an intake air amount of the internal combustion engine is varied to an opening degree according to the target air fuel ratio during the stop of the rotation of the internal combustion engine, or during the fuel cut of the internal combustion engine.
6 . The control method for the hybrid vehicle as claimed in claim 2 , wherein when the combustion mode is switched from the lean combustion to the stoichiometric combustion, at the restart of the internal combustion engine from the stop of the rotation of the internal combustion engine, or at the fuel cut recovery of the internal combustion engine, the opening degree of the throttle valve configured to control the intake air amount of the internal combustion engine is varied to the opening degree smaller than the opening degree according to the target air fuel ratio, and then the opening degree of the throttle valve is varied to the opening degree according to the target air fuel ratio.
7 . The control method for the hybrid vehicle as claimed in claim 1 , wherein when the combustion mode is switched from the lean combustion to the stoichiometric combustion, a fuel cut to stop the fuel supply to the internal combustion engine is performed, the air fuel ratio is switched to the theoretical air fuel ratio, or the air fuel ratio richer than the theoretical air fuel ratio at a fuel cut recovery at which the fuel supply to the internal combustion engine is restarted.
8 . The control method for the hybrid vehicle as claimed in claim 1 , wherein when the combustion mode is switched from the stoichiometric combustion to the lean combustion, the fuel supply to the internal combustion engine is stopped, and then the internal combustion engine is restarted by setting the target air fuel ratio to the air fuel ratio leaner than the theoretical air fuel ratio.
9 . The control method for the hybrid vehicle as claimed in claim 8 , wherein when the combustion mode is switched from the stoichiometric combustion to the lean combustion, the rotation of the internal combustion engine is stopped, and the air fuel ratio is switched to the air fuel ratio leaner than the theoretical air fuel ratio at the restart of the internal combustion engine.
10 . The control method for the hybrid vehicle as claimed in claim 8 , wherein when the combustion mode is switched from the stoichiometric combustion to the lean combustion, the fuel cut to stop the fuel supply to the internal combustion engine is performed, the air fuel ratio is switched to the air fuel ratio leaner than the theoretical air fuel ratio, at the fuel cut recovery at which the fuel supply to the internal combustion engine is restarted.
11 . A control device for a hybrid vehicle comprising:
a first motor configured to supply a generated electric power to a battery;
a second motor configured to drive a driving wheel by the electric power from the battery, or the electric power generated by the first motor;
an internal combustion engine configured to drive the first motor; and
a controller configured to switch between a stoichiometric combustion in which a target air fuel ratio of the internal combustion engine is set to a theoretical air fuel ratio, and a lean combustion in which the target air fuel ratio is set to be leaner than the theoretical air fuel ratio,
wherein when the combustion mode is switched from the lean combustion to the stoichiometric combustion while a request torque of the internal combustion engine is less than a predetermined value, the controller is configured to
stop a fuel supply to the internal combustion engine,
decrease an intake air amount of the internal combustion engine during the stop,
set the target air fuel ratio of the internal combustion engine to the theoretical air fuel ratio, or the air fuel ratio richer than the theoretical air fuel ratio, in a state in which the intake air amount of the internal combustion engine is decreased, and
restart the internal combustion engine,
wherein when the combustion mode of the internal combustion engine is switched from the lean combustion to the stoichiometric combustion while the request torque of the internal combustion engine is greater than the predetermined value, the controller is configured to switch the target air fuel ratio with the fuel supply continued.