1. Field of the Invention
The present invention relates to control devices for controlling automatic engine stop and start. The control device is capable of automatically stopping the internal combustion engine of a vehicle on receiving an automatic engine stop request and automatically restarting the internal combustion engine on receiving an engine restart request.
2. Description of the Related Art
There is a recent trend for vehicles to be equipped with an automatic engine control system capable of automatically stopping and starting the internal combustion engine of a vehicle in order to improve fuel consumption and reduce exhaust gas emission. Such an automatic engine control system is called to as the “engine idle stop control system”. The engine idle stop control system can automatically stop the engine when the driver intends to stop the vehicle, and automatically restart the engine when the driver of the vehicle operates various units in order to restart the engine, for example, the driver of the vehicle depresses the clutch pedal, releases the brake pedal, and operates a shift lever.
In general, the engine starter mounted to the internal combustion engine of a vehicle is comprised of an electric motor for pushing and rotating the pinion gear in order to engage with a ring gear fixed to the crank shaft of the internal combustion engine. This makes it possible for the pinion gear to be cranked with the ring gear fixed to the rotary shaft of the internal combustion engine of the vehicle. However, there is a possibility of generating large gear meshing noises and impacts due to the engagement when the pinion gear is meshed with the ring gear which is fixed to the crank shaft under a large difference of rotation speed between the pinion gear and the ring gear because the pinion gear cannot be smoothly meshed with the ring gear due to a large difference in rotation speed between them.
Conventional patent documents, for example, Japanese patent laid open publication No. JP 2002-122059 has disclosed a conventional technique which restarts the internal combustion engine of a vehicle by the following steps (a1) and (a2) when an engine restart request occurs when the rotation speed of the internal combustion engine is dropping immediately after the automatic engine stop of the internal combustion engine caused by the generation of an automatic engine stop request:    (a1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine when the rotation speed of the internal combustion engine (or the rotation speed of the ring gear) almost zero, namely, when the engine almost stops; and    (a2) After the step (a1), the starter motor rotates the pinion gear in order to start the cranking.
However, if the engine restart request occurs when the rotation speed of the internal combustion engine is dropping due to the automatic engine stop, the above conventional technique disclosed in JP 2002-122059 increases a delay period of time counted from the time when an engine restart request occurs to the time when the internal combustion engine is actually restarted because the cranking must be performed by the starter motor in order to restart the internal combustion engine after the rotation speed of the internal combustion engine is almost zero, namely, the engine is almost stopped. This delay period of time may cause discomfort driving to the driver of the vehicle.
In order to solve the above conventional drawback, there are other conventional techniques disclosed in Japanese patent laid open publications No. JP 2005-330813 and JP 2002-70699, which restart the internal combustion engine of a vehicle by the following steps (b1) and (b2) when the engine restart request occurs when the period of the rotation speed of the internal combustion engine is dropping due to the occurrence of the automatic engine stop request and the stop of combustion of the internal combustion engine:    (b1) The pinion gear is meshed with the ring gear which is fixed to the crank shaft of the internal combustion engine after the rotation speed of the pinion gear is synchronized with the rotation speed of the ring gear so as to decrease a difference in rotation speed between the pinion gear and the ring gear; and    (b2) After the step (b1), the starter motor starts to rotate the pinion gear in order to perform the cranking.
However, the conventional techniques disclosed in JP 2005-330813 and JP 2002-70699 only show the engagement between the pinion gear and the ring gear when they are synchronized with each other, but do not disclose and suggest any technique to detect and determine an optimum time in order to smoothly and correctly mesh the pinion gear with the ring gear. That is, the conventional techniques do not disclose and suggest any technique to detect and determine the optimum time when the pinion gear is meshed with the ring gear.