Economic ISG system and control method thereof

The method of controlling an Idle Stop & Go (ISG) system including a battery having charging and discharging durability, a battery sensor estimating the state of the battery, a reinforcing starter having durability against the increasing number of start times, a brake boosting pressure sensor, and a controller monitoring the state of the battery by using the battery sensor, restarting an engine in an idle stop state by operating the reinforcing starter with electricity from battery, determining whether to enter the idle stop state in response to a signal from the brake boosting pressure sensor, and starting/stopping the engine in accordance with the operational states of a shift lever and a brake by a driver, the method comprising:

• determining first idle stop state entry that determines whether idle stop state entering conditions are satisfied, using vehicle speed, the operational state of an acceleration pedal, and a signal from the brake boosting pressure sensor;
• determining second idle stop state entry that determines whether the shift lever is at the N-stage and the brake has been turned on after the determining first idle stop state entry;
• entering idle stop state by stopping the engine, when the shift lever is at the N-stage and the brake has been turned on, as the result of the determining second idle stop state entry;
• determining first idle stop state release that determines whether the shift lever is at the D-stage and the brake has been turned on;
• first idle stop state release that restarts the engine, when the shift lever is at the D-stage and the brake has been turned on, as the result of the determining first idle stop state release;
• after the first idle stop state release, determining second idle stop state release that determines whether the hydraulic pressure of the automatic transmission is sufficiently prepared;
• deferring idle stop state release that maintains the shift stage of the transmission at the N-stage while the hydraulic pressure of the automatic transmission is not sufficiently prepared, as the result of the determining second idle stop state release;
• and
• finishing idle stop state release that switches the shift stage of the transmission to the D-stage, when the hydraulic pressure of the automatic transmission is sufficiently prepared.