Chapter 41 - PowerPoint Presentation

Slide1

Chapter 41

Automatic

Transmissions and TransaxlesSlide2

Selects gear ratios according to engine speed, power train load, vehicle speed, and other operating factors

Most have four speeds with an overdrive fourth gear

Many have five, six, and up to eight speeds

Automatic

Transmissions and TransaxlesSlide3

Torque Converter

A fluid clutch or coupling that transfers torque from the engine to the transmission

Automatically engages and disengages power from the engine in relation to RPMSlide4
Slide5

Torque Converter (Cont.)

At idle, there is not enough fluid flow for power transfer

As RPM increases, fluid flow is sufficient to transmit engine powerSlide6

Torque Converter Internal PartsSlide7

Torque Converter Components

Impeller or Pump Assembly

Receives power from the engineSlide8

Torque Converter Components

Turbine

Transfers power to the transmission main shaftSlide9

Torque Converter Components

Stator

Is the torque multiplier

Overrunning clutch

Allows the stator to turn in only one directionSlide10

Basic Operation

Transmission fluid is the medium to transfer energy

The faster the impeller rotates, the greater energy the fluid has to transfer

The fluid leaving the impeller acts on the turbine

The turbine drives the transmission input shaftSlide11
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Types of Oil Flow

Rotary Flow

Oil flow around the circumference caused by rotation of the torque converter on its axis

Vortex Flow

Oil flow from the impeller to the turbine and back to the impeller

Coupling point is when turbine speed approaches impeller speedSlide13
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Keeps the stator from rotating when driven in one direction

The stator is locked when the there is a difference between the turbine and impeller speeds

Overrunning ClutchSlide16
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Lockup Torque Converter

Eliminates the 10% slip between the impeller and turbine

Improves fuel economy

Reduces operational temperature

Most torque converter clutches (TCC) use electronically controlled hydraulic pistonsSlide19

Lockup ClutchSlide20

Knowledge Check

Technician A says the overrunning clutch is part of the stator. Technician B says the overrunning clutch is part of the lockup clutch. Who is correct?Slide21

Planetary Gears

Used to transfer power and multiply torque

Compound gearsets spread the load over more teeth for increased strength and to obtain the largest number of gear ratios

Planetary carrier may be cast iron, aluminum, or steelSlide22

Planetary Gears (Cont.)Slide23

Ring Gear (Annulus)Has internal teeth

Sun Gear

Is located in the center of the assemblyPlanetary Carrier

Holds the planetary pinion gears

Planetary Gear ComponentsSlide24

Planetary GearsetSlide25

When the planetary carrier is the input, an overdrive condition is produced

When the planetary carrier is the output, an underdrive condition is produced

When the planet carrier is held, reverse gear is produced

Planetary Gear OperationSlide26

SimpsonHas two separate planetary gearsets with a common sun gear

Ravigneaux

Has two separate sun gears, two separate planetary gears, and a common ring gear

Types of Compound GearsetsSlide27

Simpson GearsetSlide28

Ravigneaux GearsetSlide29

Planetary Gearsets in Tandem

Some transmissions use two simple planetary gearsets in series

Gearset members are not shared

Each member has a holding deviceSlide30

Lepelletier System

Used on some six, seven, eight, and nine speed transmissions

Many are more compact than most four- and five-speed automatics

Connects a simple planetary gearset to a Ravigneaux gearset

The simple gearset is used as the inputSlide31

Nonplanetary Gearset TypeUses constant mesh gears similar to a manual transmission

Continuously Variable Type (CVT)

Has no fixed forward speeds

Uses belts and pulleys to provide variable ratios

Other Transmission DesignsSlide32

Honda Nonplanetary TransaxleSlide33

CVT TransmissionSlide34
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CVT Controls

Controls consist of the TCM, input sensors, and solenoids

A shift control valve controls pressure applied to the drive and driven pulleysSlide36

Planetary Gear-Based CVTs

Used in Toyota and Ford hybrid vehicles

Contains the motor/generators and planetary gearset

Used in the 2Mode HEV transmissionSlide37

Knowledge Check

What are the three gears the make up a planetary gearset?Slide38

Planetary Gear Controls

Certain planetary components must be held while others must be driven

Planetary control refers to transmission bands, servos, and clutchesSlide39

BandsAre typically used as a holding device

Servos

Are used to apply the bandMultiple Friction Disc Assemblies

Are used to hold or apply

Apply DevicesSlide40

Transmission Bands

A braking assembly positioned around a stationary or rotating drum or carrierSlide41

Transmission Servos

Covert hydraulic pressure into a mechanical force that applies a band

Simple servos are released by spring pressure

Compound servos are released and held by fluid pressureSlide42

Typical Simple ServoSlide43

Transmission Clutches

Able to hold and drive planetary gear members

Overrunning clutches are used to hold or drive members of the gearset

Both sprag and roller overrunning clutches are usedSlide44

Overrunning Clutches

Can be used to hold or apply members of the gearset

Are typically used as a holding device

Apply Devices (Cont.)Slide45
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Multiple-Disc Clutches

A series of friction discs and steel plates used to transmit torque or apply braking force

Internal teeth mesh with clutch hub

External teeth mesh with internal splines in transmission housing or clutch drumSlide47
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Bearings are used to reduce wear and friction

Most either slide or roll against the surface

Bushings are pressed into place

Support rotating parts, guide parts, and control fluid flow

Thrust washers may act as a bearing and a spacer to control endplay

Bearings, Bushings,

and Thrust WashersSlide50

Sliding BearingsThrust washers

Bushings

Roller BearingsTorrington

Tapered

Ball Bearings

Bearing TypesSlide51

Typical Bearing LocationsSlide52

Bushing LocationsSlide53

Torrington BearingSlide54

Snaprings

Both internal and external types are used

Internal snaprings hold servo and clutch assemblies together

May also be used to adjust clearancesSlide55

Gaskets and Seals

Gaskets

Seal two parts together or prevent fluid flow

Classified as either hard or soft gaskets

Seals

Used to seal fluid around valves, shafts, and other moving partsSlide56

Static

Is used between two parts that do not move

DynamicIs used between two parts that move with either rotating or reciprocating motion

Positive

Prevents all fluid leakage

Non-positive

Allows a controlled amount of leakage

Is used to lubricate a moving part

Seal ClassificationsSlide57

Typical Seal and Bearing LocationsSlide58

Metal Sealing Rings

Used where some leakage is acceptable

Made of cast iron, nylon, or TeflonSlide59

Final Drive Assemblies

Transmit transaxle output to the differential section

Four common configurations:

Helical gear

Planetary gear

Hypoid gear

Chain driveSlide60

Chain Final DriveSlide61

Knowledge Check

Which of the following is NOT a type of apply device?

Overrunning clutch

Band

Multidisc clutch

Thrust bearingSlide62

Hydraulic System

The fluid operates, lubricates, and cools the transmission

The pump is the source of all fluid flow

Pressure - regulating valves change fluid pressure to control shift quality and shift points

Flow - directing valves send to fluid to the correct apply device for gear changesSlide63

Fluid reservoir

Oil pan

Pressure source

Pump

Vent

Necessary to draw fluid into the pump

Transmission cooler

Removes excessive heat

Control valves

Valve body

Output devices

Apply devices

Hydraulic System ElementsSlide64
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Functions of ATF

C

ools the transmission

Cleans internal parts

ATF under pressure forces valves to move

Used to operate clutches and other apply devicesSlide66

Reservoir

Stores the ATF

The oil pan stores fluid in the automatic transmissionSlide67

Venting

The case must have a vent to atmospheric pressure

The vent allows pressure to dissipate from heat buildupSlide68

Transmission Coolers

Remove heat from the ATF

May be incorporated into the radiator

May have separate cooler

Lines connect the transmission and coolerSlide69

Valve Body

Distributes and controls pressurized fluid throughout the transmission

Made of two or three main components

Valve body

Separator plate

Transfer plateSlide70
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Check ball valves

Poppet valves

Spool valvesSlide72

Oil Pump

Driven by the drive hub of the torque converter

Gear and vane-type pumps are common

Variable displacement pumps used in some transmissionsSlide73

Governor Assembly

Used to signal upshift or downshift

Engine load may delay governor signalSlide74

Pressure Boosts

Under heavy loads, fluid pressure must be increased to increase holding capacity

Engine load can be monitored electronically or by throttle valve pressure

Older systems used a vacuum modulator to sense engine vacuumSlide75

MAP Sensor

Used to monitor engine load

Increased engine load requires changes in transmission operationSlide76

Kickdown Valve

Downshifts when the driver quickly presses the throttle wide open

Older vehicles use a kickdown cable

Modern vehicles use TP sensor inputSlide77
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Shift Quality

Shift feel is controlled by the pressure at which each hydraulic member is applied or released

Timing between band and clutch application to prevent engine flare-up or clutch and band slippageSlide79

Shift Timing

Determined by throttle pressure and governor pressure acting on opposite sides of the shift valveSlide80

Gear Changes

Gear changes occur either automatically or at the command of the driver

The transmission cannot shift into park, reverse, or neutral by itselfSlide81

Park/Neutral

When park is selected, the park pawl or lever engages the park gear

The manual shift valve blocks fluid flow to the clutches and bands

Fluid flows to cool the transmissionSlide82

Reverse

The manual shift valve allows fluid to flow to the low/reverse band

The front clutch locks, the sun gear becomes the input

The ring gear becomes the outputSlide83

Drive Range

Front clutch engages

The shift valve controls upshifting into higher gears

Once governor pressure is great enough, upshifting will occurSlide84

Automatic Downshifting

Downshifting occurs when governor pressure decreases

Can also occur with throttle pressure overcomes governor pressure