Brake bands for an automatic transmission and method for controlling a gear shift in automatic transmission and feedback loop control system

A brake band mechanism for an automatic transmission having a brake drum, said mechanism comprising:

• a brake band encircling the brake drum, said brake band including opposing ends, said brake band operable to be compressed and expanded around the brake drum;
• a linkage coupled to said brake band;
• a two-stage hydraulic servo, said linkage coupled to said servo, said servo including a servo rod position sensor for determining a position of a stroke rod of said servo, said servo providing a rapid activation of the linkage during a first stage to rapidly expand said brake band, and a controlled compression and expansion of said brake band during a second stage;
• and
• a clip structure, said clip structure being mounted to an end of said brake band and being coupled to said linkage, said servo activating said linkage to provide positive compression and expansion to said brake band for applying friction to the brake drum to control the speed of rotation of said brake drum;
• wherein said servo includes a first piston and a second piston, said first piston being smaller than said second piston, said first piston being operable to provide rapid movement of said brake band and said second piston being operable to provide fine adjustments of said brake band.

A method of controlling a shift of an automatic transmission comprising:

• providing a brake band for engaging a brake drum of an automatic transmission, said brake band being positively controlled for both apply and release pressure around said brake drum;
• applying a first fast active compression force to said brake band to a predetermined position;
• and
• providing a closed loop control of pressure on said brake band in both positive apply and release directions for controlling shift parameters of the transmission, based on a predetermined input;
• wherein a two-stage servo is used for controlling said brake band;
• wherein said servo has a first stage for rapidly applying band pressure, and a second stage for providing positive finite control of both apply and release pressures on said brake band during the shift.