AUTOMATIC TRANSMISSIONSSherief El Hadary ID:567

AUTOMATIC TRANSMISSION

Torque Converter

Hydraulic Control Unit

Planetary Gear Unit

TORQUE CONVERTER - PURPOSE

The purposes of the torque converter are to: Transmit engine

torque into the transmission

Multiply engine torque Dampen engine

pulsations Provide “flywheel”

mass

Torque converter

TORQUE CONVERTOR – CONSTRUCTION

TORQUE CONVERTOR – OPERATION

STATOR OPERATIONThe purpose of the

stator is to re-direct fluid flow to assist engine rotation during the multiplication phase

The stator must not interfere with the fluid flow during the coupling phase

ONE WAY CLUTCH

SPEED RATIOSpeed ratio is the comparison of

pump and impeller speeds expressed as a percent.

Speed ratio = pump speedturbine speed X 100

TORQUE MULTIPLICATIONTorque multiplication occurs at

speed ratios lower than 90%

Torque multiplication is highest when the torque converter is at STALL

STALL SPEEDThe torque converter is at stall

when: The turbine is stationary The pump is turning at maximum RPM

COUPLING POINTThe coupling point occurs at a

speed ratio of approximately 90% Torque multiplication is no longer

provided

VORTEX FLOWVortex flow is a

“spiraling” or rolling flow of fluid in a torque converter when the speed ratio is very low (during torque multiplication)

ROTARY FLOWRotary flow

occurs in a torque converter at high speed ratios – the fluid is simply carried along with the pump and turbine vanes

LOCK – UP TORQUE CONVERTERSIn order to

increase efficiency a hydraulically applied clutch locks the turbine to the pump case under certain conditions to remove slipping

PLANETARY GEARS - PURPOSEThe planetary

gear unit provides: A path for engine

power to get to the drive shaft / final drive

A way of changing torque, speed, and direction of the engine power

Planetary Gear Unit

GEAR RATIOGear ratio is the comparison of

input gear revolutions to achieve one output revolution

Driven gear teeth / Drive gear teeth

GEAR REDUCTIONGear reduction provides greater

output torque at reduced output speed

Gear reduction is achieved by having a small gear drive a large gear

DIRECT DRIVEDirect drive is a gear ratio which

results in transmission of input torque and speed to the output shaft without affecting the torque and speed

Direct drive is achieved with two equally sized gears

OVERDRIVEOverdrive is a gear ratio which

provides reduced output torque at a greater output speed

Overdrive is achieved by having a larger gear driving a smaller gear

PLANETARY GEAR SETSPlanetary gear sets are used to

provide: Park & Neutral Gear reduction Direct drive Overdrive Reverse

PLANETARY GEARS

PLANETARY OPERATIONIn order for the planetary gear set

to transmit power, each of the three members of the planetary gear set must be perform one of three jobs: Input Output Reaction

JOB DESCRIPTIONINPUT:

The input gear receives the engine power

OUTPUT The output gear provides drive force to

the drive shaft or final driveREACTION

The reaction member must be HELD and prevented from moving

PARK / NEUTRALPark and neutral can be achieved

by: Disconnecting the input member Disconnecting the reaction member

GEAR REDUCTION - #1In this case:

The smallest gear drives

The middle sized gear is held

The largest gear (the carrier) is driven

Result: Maximumgear reduction

GEAR REDUCTION - #2In this case:

The middle sized gear drives

The smallest gear is held

The largest gear is driven

RESULT: Gear reduction

DIRECT DRIVEIf any two

members are locked together (both providing input) direct drive occurs.

OVERDRIVEWhen the carrier

drives either other gear OVERDRIVE occurs

REVERSEReverse will only

occur if the carrier is held The sun gear

drives The ring gear is

driven

REVERSE OVERDRIVE If the ring gear was to drive the

sun gear while holding the carrier, reverse would occur in an overdrive ratio

SIMPSON GEAR SETSSimpson gear

sets use a common sun, two carriers, and two ring gears The sun, ring, and

pinions are the same size

RAVIGNEAU GEAR SETSRavigneau gear

sets use: Two sun gears

(different sizes) Two sets of pinion

gears One ring gear

RAVIGNEAU GEAR SETS

ACTUATORSActuators are used to connect

members of the planetary gear set to the: Input shaft Output shaft Transmission case

ACTUATOR TYPESThe actuators used in automatic

transmissions can be: Driving devices Brake devices

DRIVE DEVICESDriving devices are multiple disc

wet clutch packsAttach input shafts to planetary

gear set members

CLUTCH PACKS

HOLDING DEVICESHolding devices are used to control the

reaction member of a planetary gear setHolding devices can be:

Multiple disc wet clutches Brake bands One way clutches

Roller Sprag

CLUTCHES AS BRAKESClutches used as

brakes are identical in construction to clutches used as driving devices except the steels are splined to the transmission housing or case

BRAKE BANDSBand brakes use a servo piston to

apply the band around the outside of a drum

BRAKE BAND

BRAKE BAND TYPESBrake bands may be:

Single wrap Double wrap

Double Wrap Single Wrap (light)

Single Wrap (heavy)

HYDRAULIC CONTROL UNIT

The hydraulic control section of the transmission uses hydraulic pressures to control and perform shifting of the transmission gears

Hydraulic Control Unit

PUMP TYPESTransmission pumps may be:

Gear and crescent Vane Variable displacement vane

GEAR

VANE

VARIABLE DISPLACEMENT

VALVESThere are two main types of

valves used in automatic transmissions: Pressure regulating or modulating

valves Relay valves

PRESSURE REGULATIONPressure regulation is used to:

Limit the oil pressure in the transmission

Control shiftingIn addition to primary regulation,

some transmissions use a “blow off” valve to prevent overpressure

MAIN LINE PRESSUREThe first pressure developed in the

transmission is called MAIN LINE PRESSURE It is controlled by the opening point of

the pressure regulator valve All other transmission pressures are

derived from main line pressure All hydraulic devices are operated on

main line pressure

MAIN LINE REGULATION

BOOST PRESSUREUnder certain circumstances,

mainline pressure must be increased to increase the holding pressure of the hydraulic devices High torque

Reverse Low gear

High load Heavy throttle demand

“DECISION PRESSURE”In order to

“decide” what gear to be in the transmission must look at road speed and engine load – just like the driver of a manual transmission

ROADSPEED

ENGINELOAD

ENGINE LOADEngine load can be determined by

either: Throttle Pressure Modulator Pressure

THROTTLE PRESSUREThrottle pressure is:

A common means of indicating engine load and driver demands

Derived from main line pressure Controlled by the throttle valve, which

is directly linked to the throttle plate (engine intake)

THROTTLE VALVE

GOVERNOR PRESSUREGovernor pressure is:

Used as an indication or road speed Developed from main line pressure Controlled by the governor valve

GOVERNOR VALVE TYPESThe three main types of governor

valves are: Spool valve Ball bearing Shaft mounted

SPOOL GOVERNORS

BALL GOVERNORS

ACCUMULATORSThe purpose of accumulators is to

cushion the shift feel to increase customer satisfaction

ACCUMULATOR TYPESAccumulators can be:

Independent Integral Valve – type

Restrictions (fixed orifices) can also be used to increase shift feel