Automatic Transmission Basics - Home | LBCC

1 Automatic Transmission BasicsAutomatic transmissions /Transaxles contain3 Major Components or Systems1) Torque Converter2) The Planetary Gears and holding devices4) The Hydraulic ControlsSelecting the Proper ATF is CRITICALM ixing fluids can ruin a transmissionAlways look up and use specified fluidTorque ConverterWatch animation of Torque Converter at ConverterThe Impelleris also called the PumpImpeller turns with the engine crankshaftThe Turbineis driven by the centrifugal force of the The Turbine is splined to the Transmission input shaftWhen vehicle is stopped and in gear, the impeller turns and the stator does not. Torque Converter Impeller or PumpTorque Converter TurbineStator OperationThe Stator provides Torque MultiplicationWhen the engine is running and the car is stopped, the stator will lock on the One Way ClutchThe one way clutch is splined to the Transmission oil pump cover or stator shaft that does not rotateThis provides maximum torque multiplicationAt Coupling Speed the stator will spin freely on the overrunning (one way) clutchAt coupling speed, about 10% of engine RPM is lost to ATF fluid slippageTorque Converter StatorTorque Converter StatorLocking Torque ConverterLocking Torque ConverterThe torque converter clutch is applied by hydraulic pressureThe PCM will control a Torque Converter Clutch (TCC)

2 Solenoid to send ATF under pressure to the lock up clutchModern TCC solenoids are duty cycled to gradually applyThe TCC will only lock in higher gearsThe TCC will unlock under acceleration (TPS input),high load (MAP or MAF) and when braking (Brake Switch)Locking Torque ConverterTorque Converter mounting bolts are applicationspecific. Using a substitute bolt(s) can cause damage to any torque converterTorque converters generate a large amount of heat, especially under accelerationMost transmissions send ATF fluid to the Transmission cooler after it leaves the torque converterMost ATF coolers are located inside the radiator tankVehicles used to tow trailers often require an additional ATF cooler mounted in front of the radiatorThis link is an animation and explanation of Planetary Planetary gear can provide gear reduction (Underdrive)

3 Direct Drive, Overdrive, or Reverse when you hold one partstationary, or lock two parts through the Planetary Gear SetMathmagically the Carrier is the largest gear in the planetary gear gear driving large gear = Under DriveUnder Drive happens when Carrier is the OutputUnder drive increases Torque decreases SpeedLarge Gear driving Smaller gear = OverdriveOverdrive happens when the Carrier is the InputIf the Carrier is HELD, the Gear set goes to REVERSEIf you do not hold or lock any part, all gears will Freewheel and no power is transferred (neutral)Underdrive is when Carrier is the Output. Hold Ring for maximum reductionHold Sun for minimum reductionGear reduction or Underdrivewill INCREASE TORQUED irect Drive happens when ANY TWO components are locked together. This is done with multipledisc clutch packsOverdrive is when Carrier is the Input.

4 Hold Ring for maximum overdriveHold Sun for minimum overdriveReverse is when Carrier is Held. Input Ring for reverse overdrive Input Sun for reverse underdriveAutomatic transmissions use compound planetary gear sets to provide multiple gear rangesSimpson Gear trains share a common Sun gearRavigneaux Gear trains share a common Ring GearMany combinations are usedOutput of one gear set becomes Input for other gear set allowing many gear ratiosAutomatic transmissions use compound planetary gear sets are controlled by:Multiple Disc ClutchesUsed to connect rotating components togetherOne Way (overrunning) ClutchesUsed to connect rotating components together inone direction and freewheel in the other Multiplate brakes used to stop or hold Brake Bands also used to stop or holdMultiple Disc Clutches connect rotating components togetherOne Way Clutches One Way Clutches Multi plate BrakesBrake BandsValve bodies control shift timing, shift pressure,gear selection, fluid pressure!

5 Valve Body must be kept spotless clean!Valve body needs clean ATF to stay trouble NOT USE shop rags to clean oil NOT allow shop rags to contact the valve will deposit lint that can block or jam shift valves, check balls, and hydraulic use lint free paper or cloth to protect and clean around the valve body or inside any part of the Transmission .!Valve Body must be kept spotless clean!Shift pressures and shift points are controlled electronically using solenoidsUse ATF fluid level Scan Tool DVOM and Labscope to diagnose shift problems