Patent ID: 8439175

Claim:
A failure detecting apparatus for a hydraulic circuit of a gearbox, the hydraulic circuit including an oil pump, a modulator valve to reduce hydraulic pressure generated at the oil pump to modulator pressure, and a solenoid valve to generate control-signal pressure from the modulator pressure output from the modulator valve wherein the solenoid valve opens and closes an output oil passage with an electromagnetic force generated by a solenoid, the failure detecting apparatus comprising: an operating-state detector configured to detect an operating state of a subject to be controlled with the control-signal pressure output from the solenoid valve; a current setting device configured to set an electrical current supplied to the solenoid so as to close the output oil passage when the modulator valve is normal and to open the output oil passage when an open failure occurs in the modulator valve, while the solenoid valve is conductive; and a failure determining device configured to detect a failure of the modulator valve when the operating state of the subject to be detected by the operating-state detector is abnormal after a value of the electrical current to be supplied to the solenoid is set at the current setting device.