| 摘要 |
PROBLEM TO BE SOLVED: To prevent a defect of a gear change operation caused by the fact that fastening hydraulic pressure is simultaneously supplied to three friction fastening elements due to a malfunction of a hydraulic control valve, in an automatic transmission which forms respective gear change stages by fastening two friction fastening elements.SOLUTION: In a constitution in which a first gear is formed by fastening an LR brake 60 and a low clutch 40, a third speed is formed by fastening a low clutch 40 and an R35-brake 80, and a retreat speed is formed by fastening the LR brake 60 and the R35-brake 80, the constitution comprises a cut valve 121 which is switched to a first state that an original pressure port of a third linear SV 113 for controlling hydraulic pressure supplied to the R35-brake 80 to a hydraulic pressure source, and a second state that the original pressure port is discharged in pressure. When the hydraulic pressure supplied to the low clutch 40 is lower than prescribed hydraulic pressure at a gear change of 3 to 1, the cut valve 121 is brought into the second state. |
