Automatic transmission

1. 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.

2. The automatic transmission as claimed in claim 1 , wherein the control section is configured to perform the following:

detecting a travel speed of the vehicle; and

applying one of the engaging elements needed to be applied to establish a low speed forward gear, to establish an escape gear with engagement of the incorrectly-applied engaging element, when the detected travel speed is below a predetermined set speed value in the case of shifting into a neutral state.

3. The automatic transmission as claimed in claim 1 , wherein the control section is configured to identify the incorrectly-applied engaging element when the vehicle restarts from a standstill after the failure is detected.

4. 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 failure is detected; and

a directional control valve arranged in a hydraulic system to selectively inhibit supplying a hydraulic pressure for applying one of the engaging elements needed to be released to establish a first gear ratio set, and inhibit supplying a hydraulic pressure for applying another of the engaging elements needed to be released to establish a second gear ratio set; wherein when the selected gear is included in the first gear ratio set and an interlock state is present in which one of the engaging elements is incorrectly applied to hold the input rotating element and the output rotating element stationary, there is a gear higher in speed than a reference gear which is established by releasing one of the engaging elements needed to be applied to establish the selected gear; wherein when the selected gear is included in the second gear ratio set and the interlock state is present, there is no gear higher in speed than the reference gear which is established by releasing one of the engaging elements needed to be applied to establish the selected gear; and wherein the control section is configured to perform the following:

detecting the interlock state;

performing a first process of escaping from the detected interlock state when the selected gear is included in the first gear ratio set; and

performing a second process of escaping from the detected interlock state when the selected gear is included in the second gear ratio set, the second process being different from the first process.