Patent ID: 7513850

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 a normal gear ratio set and an emergency gear ratio set excluded from the 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 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 the failure is detected; wherein the control section is configured to perform the following: 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; judging in accordance with the selected gear when an interlock state is detected, whether or not it is possible to establish a gear higher in speed than a reference gear by releasing one of the engaging elements needed to be applied to establish the selected gear; shifting into a gear higher in speed than the reference gear as an escape gear when it is judged that it is possible to establish a gear higher in speed than the reference gear; and shifting into a neutral state when it is judged that it is not possible to establish a gear higher in speed than the reference gear.