Control system for compression-ignition engine

A control system comprising:

• a compression-ignition engine having a combustion chamber formed by a cylinder, a piston, and a cylinder head and configured to perform SPCCI (SPark Controlled Compression Ignition) combustion, in which spark ignition (SI) combustion and compression ignition combustion are combined;
• a fuel injection valve attached to the engine;
• a spark plug disposed to be oriented into the combustion chamber and configured to perform ignition;
• an air-fuel ratio controller configured to adjust an air-fuel ratio of mixture gas inside the combustion chamber;
• a three-way catalyst provided in an exhaust passage of the engine;
• a temperature sensor configured to detect a parameter related to a temperature of the combustion chamber;
• and
• a controller connected to the fuel injection valve, the air-fuel ratio controller, the spark plug, and the temperature sensor and configured to output a control signal to the air-fuel ratio controller upon reception of a detection signal from the temperature sensor,
• wherein the controller includes:
• a processor configured to execute:
• a temperature determining module configured to determine whether the temperature of the combustion chamber is at or above a given temperature based on an output value of the temperature sensor;
• an air-fuel ratio controlling module configured, when the temperature of the combustion chamber is determined to be below the given temperature at an engine load, to output the control signal to the air-fuel ratio controller to set the air-fuel ratio of the mixture gas to a stoichiometric air-fuel ratio and, when the temperature of the combustion chamber is determined to be above the given temperature at the engine load, to output the control signal to the air-fuel ratio controller to set the air-fuel ratio of the mixture gas leaner than the stoichiometric air-fuel ratio;
• and
• a spark plug controlling module configured to output a control signal to the spark plug to perform the ignition at a given ignition timing so that the mixture gas starts combustion by flame propagation and then unburned mixture gas self-ignites, the given ignition timing being stored in an ignition timing memory,
• wherein the controller controls the spark plug to perform SPCCI combustion so as to ignite the mixture gas at a first given timing so that the ignited mixture gas starts propagating flame along a wall of the combustion chamber by a swirl flow, and then unburned mixture gas is compressed to ignite at a second given timing,
• wherein the controller comprises the air-fuel ratio controller,
• wherein the parameter related to the temperature of the combustion chamber is an intake-air-temperature related value,
• wherein the controller has a first operating range map defining a flame propagation combustion in which self-ignition does not occur from a lowest load to a highest load of the engine, a second operating range map defining self-ignition combustion in which the air-fuel ratio is at the stoichiometric air-fuel ratio from the lowest load to the highest load of the engine, and a third operating range map defining self-ignition combustion in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio from the lowest load to a given high load of the engine, and self-ignition combustion in which the air-fuel ratio is at the stoichiometric air-fuel ratio from the given high load to the highest load of the engine, and
• wherein the controller further includes an operating range map selecting module configured to select the first operating range map when the intake-air-temperature related value is below a first low intake air temperature, the second operating range map when the intake-air-temperature related value is at or above the first low intake air temperature and below a second intake air temperature higher than the first low intake air temperature, and the third operating range map when the intake-air-temperature related value is at or above the second intake air temperature.