Power Transmission System Fail-Safe Valve Failure Detection

The system performs failure detection by supplying hydraulic pressure to both engagement devices only when the third engagement device is in the released state, establishing safe preliminary conditions before attempting detection. This preliminary check of the third engagement device state prevents the harmful tie-up condition from occurring while still enabling failure detection when safe to do so

The third engagement device serves as an intermediary safety mechanism that, when released, allows hydraulic pressure to be supplied to both first and second engagement devices for failure detection. The electronic control unit uses the state of this intermediary device to control whether failure detection proceeds, thus mediating between the need for detection and the risk of tie-up

The electronic control unit implements feedback by continuously monitoring the engagement states of the first and second engagement devices and comparing them against expected states. When both devices are simultaneously engaged (indicating fail-safe valve failure), the system provides feedback by prohibiting power transmission through the affected path, thus detecting valve failures without requiring complex additional hardware

The system uses its own existing hydraulic pressure supply mechanism and engagement device state monitoring capabilities to perform self-diagnosis of the fail-safe valve. By attempting engagement under controlled conditions and detecting the resulting state, the system serves its own failure detection needs without requiring separate dedicated detection hardware