| 主权项 |
1. A spark ignition engine comprising:
an engine body having a cylinder; a spark plug disposed to face an inside of the cylinder, and configured to ignite an air-fuel mixture in the cylinder; an exhaust returning apparatus configured to introduce an exhaust gas into the cylinder; and a controller configured to operate the engine body by controlling at least the spark plug and the exhaust returning apparatus, wherein the controller performs switching between a compression ignition mode in which compression ignition combustion is performed by auto-ignition of the air-fuel mixture in the cylinder to operate the engine body, and a spark ignition mode in which spark ignition combustion is performed by driving the spark plug to ignite and combust the air-fuel mixture in the cylinder to operate the engine body, the controller controls the exhaust returning apparatus at least in the compression ignition mode to introduce the exhaust gas into the cylinder so that an EGR ratio which is a ratio between an amount of the exhaust gas to a total amount of a gas in the cylinder is a predetermined value, and the controller reduces an amount of the exhaust gas introduced into the cylinder and increases an amount of fresh air introduced in the cylinder to reduce the EGR ratio to be lower than the EGR ratio set in the compression ignition mode, and to make an air-fuel ratio of the air-fuel mixture in the cylinder lean of a theoretical air-fuel ratio and lean of the air-fuel ratio in the spark ignition mode before switching the engine body to the compression ignition mode, and makes the ignition plug inactive, thereby switching the engine body operated in the spark ignition mode to a transitional mode in which the compression ignition combustion is performed before switching to the compression ignition mode. |
