Brake Band
 

Who can explain to me what is the job function of the brake band ?

band brake
 

this is from the subaru service manual ;band brake a: construction The band brake consists of a flex type brake band, a brake band adjusting mechinism, two servo pistons, two retainers, two return springs, a stem, a strut, and others. the band brake can be adjusted as installed on the vehicle.
b:function One end of the brake band is secured to the transmission case via the brake band adjusting screw. When no hydrolic pressure is applied to the servo piston from the hydrolic pressure controller, the servo piston and band servo piston O.D. are forced downward by the return spring, as shown in (A) of the figure.When hydrolic presasure 2A is applied to the servo chamber (11), it causes the band servo piston to come into contact with the stepped portion of the band servo piston stem ,thereby pushing the band servo piston stem upward to state (B). Under this condition, the brake band slowley tightensthe reverse clutch drum and fixes the front sun gear of the planetary gear. (@nd speed state).
Next, when the release pressure 3R to the servo chamber(1) and the hydrolic operating pressure 2A to the servo chamber (11) areapplied simultaneously, the band servo piston is pushed downward by the force of the return spring and the pressure differance between chamber(1) and chamber(2), caused by the differance in operating areas of the band servo pistons. Under this condition, state (A) is resumed, and the brake band loosens and releases the reverse clutch drum. (3rd speed state).
When hydrolic pressure 4A is applied to the servo chamber (111) under the 3rd speed condition, the band servo piston O.D. is brought into contact with the retainer installed at the lower end of the band servo piston stem. Hence, the stem is pushed upward. As a result, state (C) is achieved where the brake band slowly tightens the reverse clutch drum and fixes the front sun gear of the front planetary gear. (4th speed state) The accumulator is built into the transmission case as shown in the figure. When hydrolic pressure 2A, 3R, and 4A are appiled from the hydrolic control unit to the respective servo chambers, the hydrolic shock loads are absorbed by the accumulator. This is because the accumulator piston moves slowly, and the brake band is tightened or released slowly. This results in a smooth gearshift operation.