Torque ConvertersTorque Converters

PurposePurpose

Allow the vehicle to come to a complete Allow the vehicle to come to a complete stop without stalling the enginestop without stalling the engine

Provide torque multiplication to allow Provide torque multiplication to allow smooth acceleration from a stopsmooth acceleration from a stop

House a torque converter clutch which will House a torque converter clutch which will eliminate torque converter slippage at eliminate torque converter slippage at highway speedshighway speeds

Parts of a Torque ConverterParts of a Torque Converter

HousingHousing HubHub

ImpellerImpeller Split ring guideSplit ring guide

TurbineTurbine Split ring guideSplit ring guide

StatorStator Stator one-way clutchStator one-way clutch

Torque converter clutchTorque converter clutch Apply pistonApply piston

Parts of a Torque ConverterParts of a Torque Converter

Principles of OperationPrinciples of Operation A torque converter is a type of A torque converter is a type of fluid couplingfluid coupling There is no direct mechanical link between the There is no direct mechanical link between the

input (engine flywheel) and the output input (engine flywheel) and the output (transmission input shaft)(transmission input shaft)

The impeller (pump of the torque converter) The impeller (pump of the torque converter) forces fluid through the turbine, which forces the forces fluid through the turbine, which forces the turbine to turn turbine to turn The turbine is splined to the transmission input shaftThe turbine is splined to the transmission input shaft

Principles of OperationPrinciples of Operation

Impeller Turbine

Fluid Coupling ProblemsFluid Coupling Problems

When there is a large difference in RPM When there is a large difference in RPM between the impeller and the turbine in a between the impeller and the turbine in a fluid coupling, the fluid coming off the fluid coupling, the fluid coming off the turbine strikes the impeller opposite the turbine strikes the impeller opposite the direction of rotation, thus slowing the direction of rotation, thus slowing the impeller down (robbing power)impeller down (robbing power)

Fluid Coupling ProblemsFluid Coupling Problems

Fluid Coupling SolutionsFluid Coupling Solutions

By incorporating a stator into a fluid coupling we By incorporating a stator into a fluid coupling we can overcome the problem of turbine discharge can overcome the problem of turbine discharge oil slowing down the impelleroil slowing down the impeller

Stator

Fluid Coupling SolutionsFluid Coupling Solutions

Split Ring GuideSplit Ring Guide

Guides the fluid flow during vortex flow Guides the fluid flow during vortex flow conditionsconditions

Phases of OperationPhases of Operation

Torque multiplicationTorque multiplication Relatively low impeller (engine) RPM’sRelatively low impeller (engine) RPM’s Stator is locked into place by its one-way clutchStator is locked into place by its one-way clutch Vortex fluid flow within the converterVortex fluid flow within the converter

Coupling phaseCoupling phase Occurs at approx. 35-40 MPH under “normal” driving Occurs at approx. 35-40 MPH under “normal” driving

conditionsconditions No torque multiplicationNo torque multiplication Stator is freewheelingStator is freewheeling Turbine is spinning at approx 90% of impeller speedTurbine is spinning at approx 90% of impeller speed Rotary flow within the converterRotary flow within the converter

Torque MultiplicationTorque Multiplication

Because the turbine discharge oil is Because the turbine discharge oil is redirected so that it hits the impeller in redirected so that it hits the impeller in the direction of impeller rotation, it helps the direction of impeller rotation, it helps the engine “turn” the impeller.the engine “turn” the impeller. This is what causes torque multiplicationThis is what causes torque multiplication

Torque Multiplication Torque Multiplication Torque converters can multiply torque at a 2:1 to 3:1 Torque converters can multiply torque at a 2:1 to 3:1

ratioratio Exact amount depends on the design of the impeller, stator, and Exact amount depends on the design of the impeller, stator, and

turbine and impeller RPMturbine and impeller RPM The point at which maximum torque multiplication occurs is near The point at which maximum torque multiplication occurs is near

the stall speed of the converterthe stall speed of the converter During the torque multiplication phase, turbine speed is During the torque multiplication phase, turbine speed is

significantly lower than impeller speedsignificantly lower than impeller speed A torque converter attached to an engine producing 200 A torque converter attached to an engine producing 200

ft/lbs of torque would deliver 500 ft/lbs of torque to the ft/lbs of torque would deliver 500 ft/lbs of torque to the input shaft of the transmission (with a 2.5:1 torque input shaft of the transmission (with a 2.5:1 torque multiplication ratio)multiplication ratio)

Fluid flow is vortexFluid flow is vortex

Vortex FlowVortex Flow

During vortex flow the fluid is circulating from the During vortex flow the fluid is circulating from the impeller to the stator to the turbine and then back impeller to the stator to the turbine and then back to the impellerto the impeller

Cross-Section of Torque Converter

Vortex FlowVortex Flow

Torque MultiplicationTorque Multiplication

0

100

200

300

400

500

600

1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000

Engine RPM

Ft/

Lb

s T

orq

ue

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0.5

1

1.5

2

2.5

3

To

rqu

e M

ult

ipli

cati

on

Rat

io

Engine Torque Input Shaft Torque Torque Multiplication

Stator OperationStator Operation

Coupling PhaseCoupling Phase

As turbine (vehicle) speed increases and As turbine (vehicle) speed increases and approaches the speed of the impeller the turbine approaches the speed of the impeller the turbine discharge oil is accelerated to the point that it no discharge oil is accelerated to the point that it no longer strikes the front side of the stator blades, longer strikes the front side of the stator blades, instead it strikes the backside of the stator blade instead it strikes the backside of the stator blade causing the stator one-way clutch to unlock and causing the stator one-way clutch to unlock and the stator to freewheelthe stator to freewheel Since the stator is unlocked, fluid is not redirected and Since the stator is unlocked, fluid is not redirected and

no torque multiplication occursno torque multiplication occurs Fluid flow is rotaryFluid flow is rotary

Rotary FlowRotary Flow As the speed of the turbine approaches the As the speed of the turbine approaches the

speed of the impeller fluid flow switches from speed of the impeller fluid flow switches from vortex to rotaryvortex to rotary

After the fluid is discharged from the turbine it is After the fluid is discharged from the turbine it is not redirected by the stator, instead it rotates not redirected by the stator, instead it rotates with torque converterwith torque converter

Front-View of Torque Converter

Rotary FlowRotary Flow

Stator OperationStator Operation

Comparison Of Flow DirectionsComparison Of Flow Directions

Converter Phase TradeoffsConverter Phase Tradeoffs

Stall SpeedStall Speed

Stall speed is the engine RPM at which Stall speed is the engine RPM at which the torque converter has coupled enough the torque converter has coupled enough that with the wheels locked the engine is that with the wheels locked the engine is not able to increase RPM any further not able to increase RPM any further

Stall Speed Stall Speed Types of stall SpeedsTypes of stall Speeds

True stallTrue stallThis is the maximum rpm the engine can attain with the This is the maximum rpm the engine can attain with the

driveline completely lockeddriveline completely lockedGenerally can only be attained with a trans-brakeGenerally can only be attained with a trans-brake

Brake stallBrake stallThis is the maximum rpm the engine can attain with the This is the maximum rpm the engine can attain with the

brakes appliedbrakes appliedThe brakes generally will not have enough holding The brakes generally will not have enough holding

power to allow the engine to reach true stall speedpower to allow the engine to reach true stall speed Flash stallFlash stall

This is the rpm at which, when you accelerate at full This is the rpm at which, when you accelerate at full throttle from a dead stop the engine RPM “flashes” tothrottle from a dead stop the engine RPM “flashes” to

TCI’s recommended method of testing stall speedTCI’s recommended method of testing stall speed

Stall TestsStall Tests

CAUTIONCAUTIONDo not brake stall a converter for Do not brake stall a converter for

more than 10 seconds at a time. more than 10 seconds at a time. During a brake stall 100% of the During a brake stall 100% of the

power developed by the engine is power developed by the engine is converted in heat in the torque converted in heat in the torque converter. converter.

Wait at least 2 minutes between Wait at least 2 minutes between brake stall testsbrake stall tests

Factors Affecting Stall SpeedFactors Affecting Stall Speed Vehicle WeightVehicle Weight Vane/Fin AngleVane/Fin Angle HorsepowerHorsepower Impeller to Turbine ClearanceImpeller to Turbine Clearance Powerband/CamshaftPowerband/Camshaft Stator DesignStator Design Torque RateTorque Rate Converter DiameterConverter Diameter Gear RatioGear Ratio

Vane DesignVane DesignDepending on the design and pitch of the blades, the impeller will “scoop” the most oil at a specific RPM, thus altering the stall speed

Stator DesignStator Design

By altering the stator design, stall speed and By altering the stator design, stall speed and torque multiplication ratios can be alteredtorque multiplication ratios can be altered

Aftermarket Stock

Stator DesignStator Design

Selecting the Proper Stall Speed Selecting the Proper Stall Speed ConverterConverter

For non-stock engine-vehicle For non-stock engine-vehicle combinations the stock torque converter combinations the stock torque converter may not be optimalmay not be optimal

Work with a torque converter company to Work with a torque converter company to choose the correct torque converterchoose the correct torque converter

Remember – Torque converter design Remember – Torque converter design involves trade-offsinvolves trade-offs

Torque Converter Design TradeoffsTorque Converter Design Tradeoffs

Low Stall Speed Low Stall Speed ConvertersConverters

High Stall Speed High Stall Speed ConvertersConverters

Torque Torque MultiplicationMultiplication Low (2.0-2.5)Low (2.0-2.5) High (2.5-3.0)High (2.5-3.0)

EfficiencyEfficiency HighHigh LowLow

Heat GeneratedHeat Generated Not as MuchNot as Much A lotA lot

Best ApplicationBest Application Engines Engines producing a Lot producing a Lot of torque at low of torque at low

RPM’s RPM’s

Engines Engines producing producing

power at high power at high RPM’sRPM’s