Restart device of vehicular engine and method for controlling same

Disclosed is a system which determines the plunge timing of a pinion with detection of the revolution speed of a ring gear and the pinion by sensors after pre-rotating a starter in the middle of the stop of an engine when the engine is stopped by an idling stop operation, wherein calculation is so performed that the pinion and the ring gear come into contact with each other when the difference between the revolution speed of the ring gear and the revolution speed, which is obtained by converting the revolution speed obtained by deducting, from the revolution speed of the pinion determined from the revolution speed of a motor, the reversed revolution speed determined by the configuration of a helical spline and the action of the plunge speed of the pinion, to the revolution speed of the ring gear by the reduction ratio of the pinion and the ring gear reaches at most 180 revolutions per minute, the start of turning on a magnet switch is determined, and a plunge operation of the pinion is performed. Thus, the pinion of the starter can be gently meshed into the ring gear of the engine while the engine still rotates in the middle of the stop of the engine.