Patent ID: 7524267

Claim:
A hydraulic control apparatus for a vehicular automatic transmission in which a plurality of shift speeds having different speed ratios are achieved by selectively engaging and disengaging a plurality of hydraulic frictional engagement devices, the hydraulic control apparatus comprising: a plurality of solenoid valves which respectively correspond to respective hydraulic frictional engagement devices of the plurality of hydraulic frictional engagement devices, which output hydraulic pressure directly to the respective hydraulic frictional engagement devices, and which are controlled to achieve any one of a plurality of shift speeds; and a switching valve device which includes a first output port connected to an input port of a first solenoid valve among the plurality of solenoid valves, wherein the first solenoid valve corresponds to a hydraulic frictional engagement device among the plurality of hydraulic frictional engagement devices, and wherein the first solenoid valve is disengaged when there is a failure that may cause tie-up in the automatic transmission, a first input port to which an original pressure is supplied, a first drain port, wherein when there is no failure that may cause tie-up in the automatic transmission, communication is provided between the first output port and the first input port, and wherein when there is a failure that may cause tie-up, communication is provided between the first output port and the first drain port to achieve a specific shift speed, a second output port connected to a drain port of a second solenoid valve among the plurality of solenoid valves, wherein the second solenoid valve corresponds to a hydraulic frictional engagement device among the plurality of hydraulic frictional engagement devices, and wherein the second solenoid valve is engaged when there is a failure that may cause tie-up, a second input port to which the original pressure is supplied, and a second drain port, wherein when there is no failure that may cause tie-up in the automatic transmission, communication is provided between the second output port and the second drain port, and wherein when there is a failure that may cause tie-up, communication is provided between the second output port and the second input port, wherein the plurality of hydraulic frictional engagement devices include a first hydraulic frictional engagement device that is engaged when a shift speed of the automatic transmission is lower than or equal to a predetermined shift speed, and is disengaged when the shift speed is higher than the predetermined shift speed, and wherein the hydraulic frictional engagement device that is disengaged when there is a failure that may cause tie-up includes the first hydraulic frictional engagement device.