Control system of engine

A method for controlling an engine where compression ignition combustion is performed when an operating state of the engine is within a predetermined compression ignition range, and spark-ignition combustion is performed when the operating state of the engine is within a predetermined spark-ignition range, the engine being operatively coupled to an exhaust variable valve mechanism, the method comprising:

• controlling a fuel injector of the engine to inject a fuel at a fuel injection timing associated with the operating state of the engine;
• operating an exhaust valve via the exhaust variable valve mechanism in a first operation mode when the operating state of the engine is within the predetermined compression ignition range, said first operation mode being defined by an opening of the exhaust valve on an intake stroke so as to reintroduce an amount of burned gas into a cylinder from an exhaust port of the engine, and operating the exhaust valve via the exhaust variable valve mechanism in a second operation mode when the operating state of the engine is within the predetermined spark-ignition range, said second operation mode being defined by a closing of the exhaust valve such that a closing timing of the exhaust valve in the second operation mode is advanced from a closing timing of the exhaust valve in the first operation mode;
• and
• estimating a first state quantity inside the cylinder, wherein the first state quantity is defined as an in-cylinder EGR ratio estimation, said in-cylinder EGR ratio estimation being based on each of an external EGR ratio and an internal EGR ratio, such that the external EGR ratio is calculated as a ratio of burned gas recirculated through an EGR passage with respect to fresh air passed through a throttle valve and intake air passed through an intake valve, and the internal EGR ratio is calculated as a ratio of the amount of burned gas reintroduced into the cylinder from the exhaust port of the engine with respect to a total gas amount introduced into the cylinder;
• wherein when the operating state of the engine is switched from the predetermined compression ignition range to the predetermined spark-ignition range, compression ignition combustion is continued until the first state quantity inside the cylinder is outside the predetermined compression ignition range, whereupon the compression ignition combustion is switched to stratified spark-ignition combustion, whereupon the stratified spark-ignition combustion is continued until the first state quantity inside the cylinder is within the spark-ignition range, whereupon the stratified spark-ignition combustion is then switched to spark-ignition combustion.

A control system of an engine where compression ignition combustion is performed when an operating state of the engine is within a predetermined compression ignition range, and spark-ignition combustion is performed when the operating state of the engine is within a predetermined spark-ignition range, the control system comprising:

• a processor operatively coupled to an exhaust variable valve mechanism and a plurality of sensors;
• and
• a memory storing a plurality of modules to be executed by the processor, the plurality of modules comprising:
• a variable valve mechanism controlling module for operating an exhaust valve via the exhaust variable valve mechanism in a first operation mode when the operating state of the engine is within the predetermined compression ignition range, said first operation mode being defined by an opening of the exhaust valve on an intake stroke so as to reintroduce an amount of burned gas into a cylinder from an exhaust port of the engine, and operating the exhaust valve via the exhaust variable valve mechanism in a second operation mode when the operating state of the engine is within the predetermined spark-ignition range, said second operation mode being defined by a closing of the exhaust valve such that a closing timing of the exhaust valve in the second operation mode is advanced from a closing timing of the exhaust valve in the first operation mode;
• a fuel injection controlling module for controlling a fuel injector of the engine to inject a fuel at a fuel injection timing associated with the operating state of the engine, wherein the fuel injection controlling module controls the fuel injection to be performed on the intake stroke during the compression ignition combustion, controls the fuel injection to be performed near a compression top dead center during stratified spark ignition combustion, and controls the fuel injection to be performed during both the intake stroke and a period from a late stage of a compression stroke to an early stage of an expansion stroke during spark-ignition combustion;
• a spark ignition controlling module for controlling an ignition plug, said ignition plug configured to forcibly ignite a mixture gas, wherein the spark ignition controlling module does not control the ignition plug to forcibly ignite the mixture gas during the compression ignition combustion, and controls the ignition plug to forcibly ignite the mixture gas after the compression top dead center during stratified ignition combustion, and controls the ignition plug to forcibly ignite the mixture gas after the compression top dead center during the spark-ignition combustion;
• and
• a first in-cylinder state quantity estimating module for estimating, based on signals from the plurality of sensors, a first state quantity inside the cylinder, wherein the first state quantity is defined as an in-cylinder EGR ratio estimation, said in-cylinder EGR ratio estimation being based on each of an external EGR ratio and an internal EGR ratio, such that the external EGR ratio is calculated as a ratio of burned gas recirculated through an EGR passage with respect to fresh air passed through a throttle valve and intake air passed through an intake valve, and the internal EGR ratio is calculated as a ratio of the amount of burned gas reintroduced into the cylinder from the exhaust port of the engine with respect to a total gas amount introduced into the cylinder;
• wherein when the operating state of the engine is switched between the predetermined spark-ignition range and the predetermined compression ignition range, the fuel injection controlling module adjusts the fuel injection timing so as not to form and ignite stratified mixture gas around the ignition plug of the engine when the first state quantity has exceeded a predetermined threshold value, and the fuel injection controlling module adjusts the fuel injection timing so as to form and ignite stratified mixture gas around the ignition plug of the engine when the first state quantity has not exceeded the predetermined threshold value.