In general, in a control system for an engine (internal combustion engine), a plurality of protrusions are disposed on an outer peripheral part of a signal rotor fixed on a crank shaft at a predetermined interval, and a tooth missing part in which the protrusion is missing at a specific crank angle is formed, and a crank angle sensor is disposed so as to face the outer peripheral part of the signal rotor. The tooth missing part is detected by using an interval of crank angle signals (pulse signal) output from the crank angle sensor being longer at a position (the specific crank angle) of the tooth missing part. Further, based on the position (the predetermined crank angle) of the tooth missing part, the crank angle is determined by using the crank angle signal and a cam angle signal and a cylinder is determined, and control of the engine (for example, fuel injection control, ignition control or the like) is performed.
Further, in recent years, in a vehicle in which an engine is mounted, an engine automatic stop-and-start control system is adopted for the purpose of reducing fuel consumption, reducing exhaust emissions or the like. In the vehicle having the engine automatic stop-and-start control system, when the engine is restarted, a quick start is required compared to when the engine is normally started (for example, when the engine is started by means of turn-on-operation of an ignition switch).
Thus, for example, in Patent Literature 1 (Japanese Patent No. 4310744), the crank angle when the engine is stopped is stored as engine stopping position information, and further change history of the crank angle signal in the engine stop is stored as the engine stopping position information. Further, when the engine is started, the cylinder discrimination is performed based on the engine stopping position information when the engine is stopped and during the engine stop.
Just before the engine is stopped, the crank shaft may rotate in a forward rotation direction and a backward rotation direction. Further, in a case in which a restart request is generated before the engine is completely stopped after an engine stop request to the engine is generated once, an engine speed may become faster or slower. At this time, in the both cases, a time interval of the crank angle signals may become extremely longer than the time interval detected immediately before. Thus, even if the tooth missing part is tried to be detected based on the time interval of the crank angle signal, when the fluctuation of the rotation speed of the crank shaft is generated, a part of the time interval of the crank angle signals being longer may be erroneously detected as a crank position reference part although it is not the crank position reference part. When the crank position reference part is erroneously detected, accuracy of the detection of the crank angle or the cylinder discrimination based on the position of the crank position reference part is deteriorated, and therefore the fuel injection control or the ignition control may not be performed normally when the engine is restarted. The technique disclosed in Patent Literature 1 described above cannot prevent the erroneous detection of the crank position reference part described above.