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In an automatic transmission of an automotive vehicle equipped with a change-speed gear train capable of selectively establishing first-speed to fourth-speed drive power trains, there are provided first and second solenoid valves each in the form of a normally open valve arranged to be supplied with

In an automatic transmission of an automotive vehicle equipped with a change-speed gear train capable of selectively establishing first-speed to fourth-speed drive power trains, there are provided first and second solenoid valves each in the form of a normally open valve arranged to be supplied with fluid under pressure at its output fluid passage in a deactivated condition, third and fourth solenoid valves each in the form of a normally closed valve arranged to permit fluid under pressure discharged from its output fluid passage in a deactivated condition, a first spool valve for fail-safe arranged to disengage a first hydraulic brake of the change-speed gear train when all the solenoid valves are supplied with the fluid under pressure at their output fluid passages or when the fourth solenoid valve and either one of the first, second and third solenoid valves are supplied with the fluid under pressure at their output fluid passages, and a second spool valve for fail-safe arranged to disengage a second hydraulic brake of the change-speed gear train when the first and fourth solenoid valves are supplied with the fluid under pressure at their output fluid passages.

대표청구항 ▼

[ What is claimed is:] [1.] An automatic transmission comprising a change-speed gear train and a hydraulic control apparatus, the change-speed gear train including first and second hydraulic clutches, and a hydraulic brake, with said change-speed gear train establishing a first-speed drive power tra

[ What is claimed is:] [1.] An automatic transmission comprising a change-speed gear train and a hydraulic control apparatus, the change-speed gear train including first and second hydraulic clutches, and a hydraulic brake, with said change-speed gear train establishing a first-speed drive power train by engagement of said first hydraulic clutch and said first hydraulic brake, a second-speed drive power train by engagement of said second hydraulic clutch and said second hydraulic brake and a third-speed drive power train by engagement of said first and second hydraulic clutches;the hydraulic control apparatus including first, second and third solenoid valves respectively for controlling fluid under pressure supplied to and discharged from said first hydraulic clutch, for controlling fluid under pressure supplied to and discharged from said second hydraulic clutch, and for controlling fluid under pressure supplied to and discharged from said hydraulic brake, and a spool valve for fail-safe arranged to disengage said first hydraulic clutch when all of said first, second and third solenoid valves are supplied with the fluid under pressure at their output fluid passages, said first and second solenoid valves each being in the form of a normally open valve, and said third solenoid valve being in the form of a normally closed valve.