Coast stop vehicle and coast stop method

A coast stop method for a coast stop vehicle for stopping a drive power source during a travel of the vehicle, the vehicle including an oil pump for producing a line pressure by a rotation of the drive power source, a variator which continuously changes a speed ratio by changing a winding diameter of a belt mounted on a pair of pulleys using the line pressure, and a sub-transmission mechanism connected in series with the variator, the sub-transmission mechanism shifting stepped gear positions by changing engaged states of a plurality of frictional engagement elements using the line pressure, the method comprising:

• determining whether or not a coast stop condition holds during the travel of the vehicle;
• executing a coast stop by stopping the rotation of the drive power source and releasing an engaged one of the plurality of frictional engagement elements when the coast stop condition holds;
• and
• prohibiting the coast stop regardless of whether or not the coast stop condition holds when a prediction is made that a belt tightening force of the pulleys will fall below an engaging force of the one of the plurality of frictional engagement elements by the execution of the coast stop.

A coast stop vehicle for stopping a drive power source during a travel of the vehicle, comprising:

• an oil pump which produces a line pressure in an oil passage by a rotation of the drive power source;
• a variator which continuously changes a speed ratio by changing a winding diameter of a belt mounted on pulleys using the line pressure;
• a sub-transmission mechanism connected in series with the variator, the sub-transmission mechanism shifting discrete gear positions by changing engaged states of a plurality of frictional engagement elements using the line pressure;
• and
• coast stop means for determining whether or not a coast stop condition holds during the travel of the vehicle and for executing a coast stop to stop the rotation of the drive power source when the coast stop condition holds,
• the coast stop means including coast stop prohibiting means for prohibiting the coast stop when a prediction is made that, at a time of determining whether or not the coast stop condition holds, a belt tightening force of the pulley will fall below an engaging force of one of the plurality of frictional engagement elements in an engaged state by execution of the coast stop.