Automatic transmission and method for determining hydraulic pressure characteristics value for automatic transmission

摘要

An automatic transmission includes a plurality of frictional engagement elements for constructing plural shift stages with combinations of engagement and disengagement thereof, a control portion for controlling the engagement and the disengagement of the frictional engagement elements, a switching device switching to a learning mode for learning a precharge time, and a precharge time determination device. The precharge time determination device transits the frictional engagement elements to an engagement side by maintaining the hydraulic pressure for determining the precharge time at a first precharge pressure while maintaining input shaft rotational speed at the learning mode at a vehicle stop state. A first precharge time defined from a start of maintaining the first precharge pressure until variation of an input value assumes significant is obtained. And a second precharge time at a second precharge pressure is obtained to be set for learning by a predetermined formula.