An automatic transmission control apparatus controls a gear position by engaging and disengaging multiple frictional elements. A hydraulic pressure detector detects hydraulic pressure applied to the frictional elements. A failure determiner determines a failure, i.e., a dual-engagement of the frictional elements in accordance with detection signals of the hydraulic pressure detector. The hydraulic pressure detector detects first and second hydraulic pressure applied to the plurality of frictional elements. The second hydraulic pressure is greater than the first hydraulic pressure. The failure determiner determines a failure in accordance with a detection signals of the first and second hydraulic pressure detected by the hydraulic pressure detector.

Disclosed is a hydraulic control system for an automatic transmission which includes a line pressure controller for regulating hydraulic pressure generated by a hydraulic pump to line pressure, a damper clutch controller for actuating a damper clutch of the torque converter, a reducing pressure controller for reducing line pressure, a range controller for selectively supplying line pressure to lines corresponding to respective shift ranges, a shift controller for supplying hydraulic pressure from the range controller to lines corresponding to respective shift ranges, a hydraulic pressure controller for converting hydraulic pressure from the range controller to operational pressure operating the friction element, and a hydraulic pressure distributor for determining a hydraulic flow path corresponding to each shift range by operating valves according to the hydraulic pressure from the shift controller, and suitably distributing the operational pressure to each friction element, wherein the shift controller further includes an additional shift control valve easily controlling timing of pressure supply and reducing a change in hydraulic pressure levels.

A manual valve body is provided with a first port communicated with a regulator valve via a pressure line, a second port connected to a first pressure control valve and a second fail safe valve so as to supply hydraulic pressure thereto at range "P", a third port connected to the regulator valve, an N-R control valve, and first and second switch valves so as to supply the hydraulic pressure from the first port thereto at range "R", a fourth port connected to second and third pressure control valves and the first and second switch valves so as to supply the hydraulic pressure from the first valve thereto at ranges "2", "3", and "D", and a fifth port connected to the first switch valve so as to supply the hydraulic pressure from the first port thereto at range "L".

A control system for an automatic transmission comprises a forward/reverse selection hydraulic servomechanism 70, a D inhibitor valve, which controls the supply of a line pressure to the servo-oil chambers of this servomechanism, and a plurality of solenoid valves 81.about.85, which are used for controlling the actuation of the shift valves and the D inhibitor valve. This control system comprises a first neutral mode and a second neutral mode for a neutral range. In the first neutral mode, the D inhibitor valve is switched to a forward drive position, and the forward drive servo-oil chamber is connected to a drain. In the second neutral mode, the D inhibitor valve is switched to a reverse drive position, and the forward drive and reverse drive servo-oil chambers are both connected to the drain.

An automatic transmission comprises a plurality of clutches 11.about.15, which are provided to select power transmission paths, respectively, in a parallel shaft speed change mechanism TM and a plurality of shift valves 60.about.68, which are used for controlling the supply and drain of hydraulic pressure to and from these clutches. For this automatic transmission, a control system comprises a forward/reverse selection hydraulic servomechanism 70 and a plurality of solenoid valves 81.about.85, which are used for controlling the supply and drain of a line pressure so as to control the actuation of these shift valves and the forward/reverse selection hydraulic servomechanism. The system further comprises a hydraulic switch 93 which detects the hydraulic pressure supplied into the right side oil chamber 73 of the forward/reverse selection hydraulic servomechanism 70 and a hydraulic switch 92 which detects the hydraulic pressure of the SECOND speed clutch 12, whose pressure is generated from the pressure in the right side oil chamber 73. The system determines whether the forward drive range is set correctly or not, based on a result of pressure detection by these hydraulic switches 92 and 93.