Engine control apparatus to predict engine speed accurately

An engine control apparatus that predicts a speed of an engine in a period of time between start of a drop in speed of the engine resulting from stop of combustion of fuel in the engine and stop of rotation of the engine, the engine control apparatus comprising:

• an electronic control unit configured to:
• predict a future speed of the engine in a normal rotation range of the engine as a function of a loss energy in a latest one of engine rotation pulsating periods, each of the engine rotation pulsating periods corresponds to a cycle of a change in speed of the engine based on increasing and decreasing a volume of a cylinder of the engine;
• determine and reverse a positive or negative sign of a value of a friction component of the loss energy in the normal rotation range, the friction component being based on mechanical friction on a piston in the cylinder of the engine during stroke of the piston in the cylinder of the engine, the value of the friction component with the sign reversed being the value of the friction component the reverse rotation range;
• calculate a loss energy in the reverse rotation range of the engine as a function of (i) the value of the friction component in the reverse rotation range, and (ii) a pumping loss component that is an energy loss based on a pressure change during an intake stroke of the engine in the reverse rotation range;
• predict a future speed of the engine in the reverse rotation range of the engine based on the loss energy in the reverse rotation range of the engine;
• and
• automatically stop the engine in response to satisfying a predetermined automatic engine stop condition, and rotate an output shaft of the engine using a starter device to restart the engine in response to a satisfying a predetermined engine restart condition after the engine is automatically stopped;
• and
• a starter controller controlling a time at which the starter device is energized based on either:
• (i) the predicted future speed of the engine in a normal rotation range of the engine, or (ii) the predicted future speed of the engine in the reverse rotation range of the engine.