Patent ID: 7749122

Claim:
An automatic transmission comprising: a planetary gear arrangement including a plurality of rotating elements, and including an input rotating element adapted to be connected to a driving source of a vehicle and an output rotating element adapted to be connected to a drive wheel set of the vehicle; a plurality of engaging elements each arranged to vary an engagement state among the rotating elements of the planetary gear arrangement in such a manner to establish at least a normal gear ratio set; and a control section configured to perform the following: selecting a gear from the normal gear ratio set in accordance with a running state of the vehicle under normal operating conditions; controlling the engagement state of each of the engaging elements in such a manner to shift into the selected gear; detecting an interlock state in which one of the engaging elements is incorrectly applied to hold the input rotating element and the output rotating element stationary; establishing, when the interlock state is detected, an escape gear by releasing one of the engaging elements needed to be applied to establish the selected gear; and identifying the incorrectly-applied engaging element in accordance with the running state of the vehicle resulting from establishing the escape gear, wherein the escape gear is included in an escape gear ratio set including at least an emergency gear ratio set excluded from the normal gear ratio set.