Control system with band brake actuator for automatic transmission

A control system for controlling a shift operation of an automatic transmission for an automotive vehicle comprising:

• a first frictional coupling element, said first frictional coupling element being locked under hydraulic pressure;
• a second frictional coupling element provided with a lock pressure chamber and an unlock pressure chamber, said second frictional coupling element being locked when hydraulic pressure is developed in said lock pressure chamber only and unlocked when hydraulic pressure is developed in said unlock pressure chamber and when hydraulic pressure is released from both said lock pressure chamber and said unlock pressure chamber;
• and
• control means for (a) supplying hydraulic pressure to said first frictional coupling element so as to lock said first frictional coupling element, (b) releasing hydraulic pressure from said lock pressure chamber of said second frictional coupling element so as to unlock said second frictional coupling element when it is necessary for said automatic transmission to shift into a predetermined gear, (c) detecting an input speed of said automatic transmission to release hydraulic pressure from said lock pressure chamber of said second frictional coupling element so as to unlock said second frictional coupling element when it is necessary for said automatic transmission to shift into a predetermined gear when input speeds of said automatic transmission higher than a predetermined speed are detected and (d) supplying hydraulic pressure into said unlock pressure chamber of said second frictional coupling element so as to unlock said second frictional coupling element when it is necessary for said automatic transmission to shift into a predetermined gear when input speeds of said automatic transmission which are lower than said predetermined speed are detected.