Drive and reverse clutch piston D RCP

(Fig. 5.24) Directing line pressure behind the drive and reverse clutch piston applies the clutch, thereby transmitting torque from the torque converter turbine output shaft to the forward sun gear. When the forward clutch is also applied, the forward planetary gears (annular, planet and sun gears) are locked together and they rotate bodily, thus producing a straight through 1:1 third gear drive. However, when the first and reverse clutch is applied instead of the forward clutch, the reverse planetary carrier is held stationary causing the reverse gear reduction ratio to be engaged.

The timing of the release of one set of gears and the engagement of another to produce smooth up and down gear shifts between second and third gears is achieved by carefully controlling the delivery and exhaustion of hydraulic fluid from the clutch and band brake servo.

These operating conditions are explained under second gear band servo.

Second gear band servo (2GBS) (Fig. 5.24) This is a double acting piston servo which has a small piston area to apply the band brake and a large piston area which is on the release spring chamber side of the servo.

Directing line pressure to the small piston area chamber of the servo applies the band brake against the resistance of the return spring and thereby holds stationary both sun gears. Introducing line pressure on the large piston area spring chamber side of the servo produces an opposing force which releases the grip on the band brake. The piston returns to the 'off' position and the relaxing of the band brake is made possible by the difference in piston area on each side, both sides being subjected to the same line pressure. The band brake is applied only in the second gear forward speed range.

During upshift from 2-3 it is important that the second gear band brake does not release too quickly relative to the drive and reverse clutch engagement, in order to avoid run-up (rapid engine speed surge) during the transition from 2nd to 3rd gear. During downshift it is also important that the second gear band brake does not engage before the drive and rear clutch releases in order to avoid tie-up (gear jamming) on the 3-2 shift.

The 3-2 control valve and the 3-2 kickdown valves therefore affect the timing relationship between the second gear band servo and the drive and reverse clutch to provide correct shift changes under all operating conditions.

First gear one way clutch (OWC) (Fig. 5.13(a)) When in drive range, the one way roller type clutch operates in place of the first and reverse multiplate brake to prevent the rotation of the reverse pinion carrier. This one way clutch enables the gear set to freewheel on overrun and to lock-up on drive, therefore preventing a jerky gear ratio in 1-2 upshift and 2-1 downshift.

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