Patent attributes
An automatic transmission includes a planetary gear arrangement, and 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 a normal gear ratio set and an emergency gear ratio set excluded from the normal gear ratio set. A control section of the automatic transmission performs the following: selecting a gear from the normal gear ratio set in accordance with a running state of a 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 a failure in the engaging elements; selecting an escape gear ratio set from the normal gear ratio set and the emergency gear ratio set; and driving the vehicle with the escape gear ratio set when a failure is detected in the engaging elements.
