SPEED-CHANGE CONTROL DEVICE OF AUTOMATIC TRANSMISSION

PROBLEM TO BE SOLVED: To accurately detect a failure when a failure occurs in a hydraulic circuit system, and assure smooth start when the failure occurs. SOLUTION: A group of speed-change control valves for performing hydraulic supply control to LOW to 5TH clutches are constituted of three linear solenoid valves, four shift valves, two cut valves, and three ON/OFF solenoid valves. The shift valves and the cut valves make the selection of an oil pathway so that a line pressure PL or a speed-change control hydraulic pressure is supplied to the clutch in an alternative manner. Then the ON/OFF solenoid valves control the operation of a shift valve. In the LOW-travelling mode, the difference in rotational speed between the rotational speed Nm of a main shaft at the time of travelling in the fifth gear and the rotational speed NM of the main shaft at the time of actual travelling is computed. When the difference in rotational speed is within a predetermined range and continues for a period greater than or equal to predetermined time, the LOW-travelling mode is judged as a 5TH travelling mode, and LOW travelling is inhibited. COPYRIGHT: (C)2007,JPO&INPIT