An automatic transmission changes gear ratios automatically as the vehicle accelerates or decelerates, freeing the driver from manually shifting gears. It has planetary gear sets to provide various forward and reverse gears, a torque converter to transmit torque like a clutch, and a hydraulic system with fluid, pumps, valves and clutches to control the gear shifts. The transmission fluid pressurized by the oil pump is directed by the valve body to shift valves and clutches/bands to smoothly shift between the transmission's 3-4 forward gears and reverse gear based on vehicle speed and throttle position.

2. What is automaticWhat is automatic
transmissiontransmission??
 Changes gear ratios automaticallyChanges gear ratios automatically
as the vehicle accelerate oras the vehicle accelerate or
deacceleratedeaccelerate
Freeing the driver from having toFreeing the driver from having to
shift gears manuallyshift gears manually
So there is no clutch pedal in anSo there is no clutch pedal in an
automatic transmission carautomatic transmission car

3. Gear-shift modeGear-shift mode

4. automatic transmissionautomatic transmission
operationsoperations
MostMost A/T have 3 or four forward speed, PARK, NEUTRAL, andA/T have 3 or four forward speed, PARK, NEUTRAL, and
REVERSEREVERSE
ItIt starts the vehicle in 1starts the vehicle in 1stst
gear. Then it shifts to 2gear. Then it shifts to 2ndnd
, 3, 3rdrd
& 4& 4thth
without assistance from driver . This happen automatically aswithout assistance from driver . This happen automatically as
vehicle speed increases & the engine load or throttle openingvehicle speed increases & the engine load or throttle opening
decreases.decreases.
ToTo slow and stop the vehicle the driver only needs to releaseslow and stop the vehicle the driver only needs to release
accelerator pedal or apply brake.accelerator pedal or apply brake.
TheThe A/T disengages the torque converter clutch & automaticallyA/T disengages the torque converter clutch & automatically
to downshifts until 1to downshifts until 1stst
gear and when the vehicle stops.gear and when the vehicle stops.

5. The main componenTsThe main componenTs
Planetary gear setsPlanetary gear sets that provide the various forwardthat provide the various forward
gear ratios as well as reversegear ratios as well as reverse
Torque converterTorque converter which acts like a clutch to transmitwhich acts like a clutch to transmit
torque while the engine is still runningtorque while the engine is still running
Hydraulic systemHydraulic system which uses a special transmissionwhich uses a special transmission
fluid sent under pressure by an Oil pump to controlfluid sent under pressure by an Oil pump to control
thethe ClutchesClutches and theand the planetary gear setsplanetary gear sets
GovernorGovernor andand ModulatorModulator oror Throttle valveThrottle valve thatthat
monitor speed and throttle position in order tomonitor speed and throttle position in order to
determine when to shiftdetermine when to shift

6. planeTary gear seT
•In Neutral, Motion of input shaft turns the Planet gears against the sun
gear, it will just spin free and have no effect on the output shaft
•In Gear Clutch pack , in this case, lock the output shaft with the sun gear
forcing both to turn at the same speed place the unit in.

7. Torque converTerTorque converTer --
principleprinciple• Large nut shaped device that is mounted between the engine and the
transmission
• It uses oil or transmission fluid to transmit power.

8. The hyDraulic sysTem
• Complex maze of tubes that sends fluid under under pressure
to all parts of the transmission and torque converter.
• Transmission fluid serves in shift control, general lubrication
and transmission cooling so to keeps the transmission at
normal operating temperature
• OIL PUMP
• VALVE BODY
• SHIFT VALVES
• BANDS

9. Oil Pump(Gear Pump)Oil Pump(Gear Pump)
• Produce all the oil pressure that is
required in the transmission
• The oil is then send under
pressure to the valve body and the
rest of the components, as required.

10. Valve BodyValve Body
• The brain of the automatic
transmission
• Contains a maze of channels
and passages that direct
hydraulic fluid to the
numerous valves
• These valves activate the
appropriate clutch pack or
band servo to smoothly shift
to the appropriate gear for
each driving situation.

11. Shift Valves
• Supply hydraulic pressure to
the clutches and bands to
engage each gear
• Determines when to shift from
one gear to the next

12. GOVERNERGOVERNER
Connected to the output shaftConnected to the output shaft
and regulates hydraulicand regulates hydraulic
pressure based on vehiclepressure based on vehicle
speedspeed

13. COMPUTER CONTROLLSCOMPUTER CONTROLLS
• Detect such things as throttle position, vehicle speed,Detect such things as throttle position, vehicle speed,
engine speed, engine load, etc.engine speed, engine load, etc.
• Downshifting automatically when going downhill.Downshifting automatically when going downhill.
• Up shift when braking on a slippery surface.Up shift when braking on a slippery surface.

14. Comparison with manualComparison with manual
transmissiontransmission
•Smooth OperationSmooth Operation
•Ease of controlEase of control
•Infinite number of gearing availableInfinite number of gearing available
•Minimum power losses during gear shiftingMinimum power losses during gear shifting
Higher cost, lower fuel efficiencyHigher cost, lower fuel efficiency
Complicated designComplicated design
Possibility of oil leakagePossibility of oil leakage

15. THANK YOUTHANK YOU