| 摘要 |
An automatic transmission is provided to release all frictional elements according to a rotational speed of a predetermined rotational element except for an input shaft and an output shaft. An automatic transmission includes a plurality of planetary gears(G1-G4) having a plurality of rotational elements and a plurality of frictional elements formed to stop selectively the rotation of the rotational elements or to rotate selectively the rotational elements. The automatic transmission realizes a plurality of gear positions by controlling an engaging state and a releasing state of the frictional elements according to instructions, changes a rotational speed of an input shaft(Input), and outputs the changed rotational speed to an output shaft(Output). A rotational speed detection unit detects a rotational speed of a predetermined rotational element except for the input shaft and the output shaft of the rotational elements. A frictional element release unit releases all of the frictional elements when the rotational speed of the predetermined rotational element is higher than a predetermined rotational speed.
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