Engine start device

An engine starting device for an automatic idle-stop system for performing idle-stop when a predetermined idle-stop condition is satisfied and for restarting an engine when a restart condition is satisfied, comprising:

• a crank-angle sensor for detecting a crank angle of the engine;
• a ring gear connected to a crankshaft of the engine;
• a ring-gear rpm detecting section for detecting an rpm of the ring gear;
• a starter motor for starting the engine;
• a pinion gear for transmitting rotation of the starter motor to the ring gear;
• a pinion-gear push-out section for pushing out the pinion gear to bring the pinion gear into meshing engagement with the ring gear;
• and
• a pinion-gear push-out control section for driving the pinion-gear push-out section to bring the pinion gear and the ring gear into meshing engagement when the ring-gear rpm detected by the ring-gear rpm detecting section becomes smaller than a predetermined threshold value,
• wherein the predetermined threshold value is determined by at least one of the crank angle, a gear range, and the restart condition.