Engine automatic stop and restart apparatus

An engine automatic stop and restart apparatus which automatically stops an engine when an automatic stop condition is satisfied, and then restarts the engine when a restart condition is satisfied, the engine automatic stop and restart apparatus comprising:

• a starter motor which rotates when supplied with electricity;
• a pinion gear provided to a rotation shaft of the starter motor;
• a plunger which pushes the pinion gear in a direction of the rotation shaft so that the pinion gear engages with a ring gear provided to a crank shaft of the engine;
• a solenoid which moves the plunger in the direction of the rotation shaft when supplied with electricity;
• a start control unit which connects a power supply to the starter motor in response to a first drive signal so that the starter motor is supplied with electricity, and which connects the power supply to the solenoid in response to a second drive signal so that the solenoid is supplied with electricity;
• a crank angle sensor which detects a crank angle of the engine, to output a crank angle signal;
• a fuel injection unit which injects fuel into the engine;
• an rpm table which describes a relationship between a power supply period of the starter motor and an estimated rpm of the pinion gear;
• and
• an engine control unit which is configured to:
• control the fuel injection unit to inject the fuel into the engine after a restart process is started, and output a first drive signal to the start control unit to start supplying electricity to the starter motor and to start measuring of the power supply period of the starter motor;
• output a second drive signal to the start control unit to start supplying electricity to the solenoid when an absolute value of a rpm difference between an rpm of the engine calculated based on a period of the crank angle signal, and an estimated rpm of the pinion gear, determined from the rpm table based on the measured power supply period, becomes smaller than a rpm difference threshold value at which the pinion gear and the ring gear can be engaged with each other;
• judge that the engine is self-resumed when the engine becomes capable of self rotation with only supplied fuel when the engine rpm calculated based on the period of the crank angle signal is larger than the estimated rpm of the pinion gear determined from the rpm table based on the measured power supply period;
• and
• stop outputting the first drive signal to the start control unit to finish supplying electricity to the starter motor when it is judged that the engine is self-resumed, finish measuring the power supply period of the starter motor, and stop outputting the second drive signal to the start control unit to finish supplying electricity to the solenoid.