Automatic Transmission Fundamental

    An automatic transmission performs the same functions as manual transmission, butit shifts gears and releases the clutch automatically.  Most modern vehicles use anautomatic transmission because it saves the driver from having to move a shift lever anddepress a clutch pedal.

    Fig. 9.5 shows the basic parts of automatic transmission.

    Torque converter - fluid coupling that connects and disconnects engine and transmissions

    Input shaft - transfers power from the torque converter to the internal drivemembers and gear sets

    Transmission oil pump - produces pressure to operate the hydraulic componentsin the transmission

    valve body - operated by shift lever and sensors, controls oil flow to the pistonsand servos

    Pistons and servos - actuate bands and clutches

    Planetary gearsets - provide different gear ratios and reverse gear

    Bands and clutches - apply clamping pressure to different parts of the planetarygearsets to operate them

    Output shaft - transfers engine torque from the gearsets to the drive shaft