Automatic transmission

1. An automatic transmission comprising:

a speed changer having a plurality of engagement elements and configured to shift the speed changer into a selected one of a plurality of shift stages by switching engaged and disengaged states of the engagement elements;

a first rotation sensor for detecting input rotation of the speed changer and for outputting a pulse signal indicating the input rotation;

a second rotation sensor for detecting output rotation of the speed changer and for outputting a pulse signal indicating the output rotation; and

a controller comprising:

an input-torque-change decision section for determining whether a change in input torque inputted into the speed changer occurs; and

an interlock decision section for executing an interlock decision on whether interlock occurs in the speed changer,

wherein the interlock decision section is configured to determine that interlock has occurred in the speed changer, when there is no pulse signal output from the second rotation sensor though, during a vehicle stopped state, the input-torque change has occurred and the pulse signal from the first rotation sensor has been outputted.

2. The automatic transmission as claimed in claim 1 , wherein:

the interlock decision section is configured to determine that interlock has occurred in the speed changer, when there is no pulse signal output from the second rotation sensor though, under a condition where the vehicle is in the stopped state and the input rotation of the speed changer is less than or equal to a predetermined speed value, the input-torque change has occurred and the pulse signal from the first rotation sensor has been outputted.

3. The automatic transmission as claimed in claim 1 , further comprising:

a non-stage speed-change mechanism constructed by variable-width primary and secondary pulleys and a belt running in the primary and secondary pulleys; and

a third rotation sensor for detecting rotation of the primary pulley,

wherein the speed changer is arranged in series with an output side of the non-stage speed-change mechanism, and the first rotation sensor is configured to detect a revolution speed of the secondary pulley.

4. The automatic transmission as claimed in claim 1 , further comprising:

a road-grade detection section for detecting whether the vehicle is stopped on a slope way whose grade angle is greater than a predetermined grade angle;

a brake-release detection section for detecting whether brakes of the vehicle have been released; and

a decision-stop section for temporarily stopping the interlock decision, executed by the interlock decision section on whether or not interlock occurs, for a predetermined time period, when it is detected by the road-grade detection section that the vehicle is stopped on the slope way whose grade angle is greater than the predetermined grade angle and it is detected by the brake-release detection section that the brakes of the vehicle have been released.

5. The automatic transmission as claimed in claim 1 , further comprising:

a torque-down control section for executing torque-decrease control that decreases an upper limit of a driving force produced by a prime mover of the vehicle, when it is determined that interlock has occurred in the speed changer.

6. The automatic transmission as claimed in claim 1 , further comprising:

a limp-home control section for executing limp-home control that enables the vehicle to run, when the input torque is exceeding a given torque value and there is no pulse signal output from the second rotation sensor for a given time after having been determined that interlock has occurred.