Patent attributes
A hydraulic control circuit for an automatic transmission of a vehicle, the transmission including hydraulically operated coupling devices at least one of which is selectively operated to establish a corresponding one of speed steps, the hydraulic control circuit including electromagnetic valve devices which output respective hydraulic pressures to operate the hydraulically operated coupling devices, respectively, an all-fail detecting and switching valve device which is switched, based on an all-fail state of the electromagnetic valve devices in which none of the electromagnetic valve devices output the respective hydraulic pressures, to an operation state corresponding to a fail position to output, as a first hydraulic pressure, a source hydraulic pressure to a first hydraulically operated coupling device out of the plurality of hydraulically operated coupling devices, and an operation-state memory valve which is switched, based on a state of the vehicle before the all-fail state occurs, from a non-running position indicating that the vehicle is not running, to a running position indicating that the vehicle is running, which is kept at one of the non-running position and the running position, and which supplies an operating hydraulic pressure to one of a second and a third hydraulically operated coupling device out of the plurality of hydraulically operated coupling devices that corresponds to the one of the non-running position and the running position at which the operation-state memory valve is kept.
