Patent ID: 7835843

Claim:
An abnormality determining apparatus of an automatic transmission which establishes a specified gear speed from a plurality of gear speeds having different gear ratios, comprising: an electronic control unit configured to calculate an actual gear ratio based on an input shaft rotation speed of the automatic transmission and an output shaft rotation speed of the automatic transmission, and determine that there is an abnormality in the gear ratio when the actual gear ratio is outside of a gear ratio range that is preset based on the specified gear speed; calculate an input shaft synchronous rotation speed based on the output shaft rotation speed and the gear ratio of the specified gear speed, and determine that there is an abnormality in the gear ratio when the difference between the input shaft rotation speed and the input shaft synchronous rotation speed is outside of a preset rotation speed range; determine whether the output shaft rotation speed is in a high rotation speed region or a low rotation speed region with respect to a reference rotation speed at which an upper limit value of the input shaft rotation speed in a rotation speed range of a higher one of the gear speeds, does not exceed a lower limit value of the input shaft rotation speed in a rotation speed range of an adjacent lower one of the gear speeds; and determine whether there is an abnormality in the gear ratio by selecting an abnormality determination when the output shaft rotation speed is in the low rotation speed region, and selecting an abnormality determination when the output shaft rotation speed is in the high rotation speed region.