FAIL SAFE HYDRAULIC SYSTEM OF AUTOMATIC TRANSMISSION OF VEHICLE

摘要

PURPOSE: A fail safe hydraulic system of an automatic transmission is provided to realize a safe travel by preventing the occurrence of interlock in a power train regardless of the sticking position of a valve spool. CONSTITUTION: A second clutch(C2) and a first brake(B1) are supplied with the output pressure of a C2/B1 control valve(52) controlled by a C2/B1 control solenoid valve(50). The output pressure of the C2/B1 control valve is switched to two paths by a C2/B1 switch valve(54). One of the paths is communicated with the second clutch via a first fail safe valve(56) while the other path is communicated with the first brake via a second fail safe valve(58). The hydraulic pressure supplied to the second clutch is discharged via the C2/B1 switch valve and the fist fail safe valve. The hydraulic pressure supplied to the first brake is discharged via the C2/B1 control valve and the second fail safe valve. The output pressure of a C1 control valve(62) is applied to a first clutch via two paths. One of the paths is communicated with a first clutch(C1). The other path operates as a control pressure to second and third fails safe valves(58,64) and supplies hydraulic pressure to a first friction element via a first shuttle valve. Then, first and second brake pressures are released. The first brake pressure generated in the C2/B1 switch valve is supplied only when the second fail safe valve is switched over.