Patent ID: 8636620

Claim:
An automatic transmission which changes and outputs an output revolution speed of a driving source that outputs a driving torque in a vehicle, the automatic transmission comprising: a transmission control section that performs a control so that a transmission ratio defined as a ratio of an input revolution speed of the automatic transmission with respect to an output revolution speed of the automatic transmission becomes a target transmission ratio; a slip control section that slip-controls a frictional engagement element in the automatic transmission so that the input revolution speed of the automatic transmission becomes a value obtained by multiplying the output revolution speed of the automatic transmission by the target transmission ratio also adding a predetermined slip revolution speed; and an abnormality judgment section that judges that; (a) when the slip control is not in progress, if an actual transmission ratio is out of a predetermined range of the target transmission ratio, abnormality occurs in the automatic transmission, and (b) when the slip control is in progress, if a value obtained by correcting the actual transmission ratio on the basis of the slip revolution speed is out of the predetermined range of the target transmission ratio, the abnormality occurs in the automatic transmission.