Hydrodynamic Drive Unit -2

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Hydrodynamic Drives

KALASALINGAMUNIVERSITY

T.SENTHIL MUTHU KUMAR,

ASSISTANT PROFESSOR,DEPARTMENT OF AUTOMOBILE ENGINEERINGKALASALINGAM UNIVERSITY


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At the end of this training session you will havelearned;

Three Phase Inverter MotorFLUID COUPLING

Transfers power smoothly

from the engine to thetransmission

Mounted on the flywheeland always rotates with it.

So it is also called fluidflywheel Consists of Pump andTurbine

Both are opposed to eachother and enclosed incasing


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WORKING OF FLUID COUPLING

Hydraulic Fluid is

contained in the casing

When engine starts , thepump starts rotating

Vanes inside the pumpdraws the oil inside at thecentre and throws out

Fluid emerges fromvanes of pump to theturbine exerting thrust

The turbine starts rotatingand picks up speed


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UNDERSTANDING FLUID COUPLING

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TORQUE CONVERTERS - PURPOSE

Allow the vehicle to come to a complete stop

without stalling the engine

Provide torque multiplication to allow smooth

acceleration from a stop

House a torque converter clutch which willeliminate torque converter slippage at highwayspeeds

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PARTS OF A TORQUE CONVERTER

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A torque converter is a type offluid coupling

There is no direct mechanical link between theinput (engine flywheel) and the output(transmission input shaft)

The impeller (pump of the torque converter)forces fluid through the turbine, which forces theturbine to turn

The turbine is splined to the transmission input shaft

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PROBLEMS FLUID COUPLING

When there is a large difference inRPM between the impeller and the turbinein a fluid coupling, the fluid coming off theturbine strikes the impeller opposite the

direction of rotation, thus slowing theimpeller down (robbing power)

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SOLUTIONS

By incorporating a stator into a fluid coupling we can

overcome the problem of turbine discharge oil slowingdown the impeller

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SOLUTIONS FLUID COUPLING

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PHASES OF OPERATION

Torque multiplication

Relatively low impeller (engine) RPMs Stator is locked into place by its one-way clutch

Vortex fluid flow within the converter

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

conditions

No torque multiplication

Stator is freewheeling Turbine is spinning at approx 90% of impeller speed

Rotary flow within the converter

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TORQUE MULTIPLICATION

Because the turbine discharge oil is redirected

so that it hits the impeller in the direction ofimpeller rotation, it helps the engine turn theimpeller.

This is what causes torque multiplication

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

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

turbine and impeller RPM

The point at which maximum torque multiplication occurs is nearthe stall speed of the converter

During the torque multiplication phase, turbine speed issignificantly lower than impeller speed

A torque converter attached to an engine producing 200ft/lbs of torque would deliver 500 ft/lbs of torque to theinput shaft of the transmission (with a 2.5:1 torque

multiplication ratio) Fluid flow is vortex

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VORTEX FLOW

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During vortex flow the fluid is circulating fromthe impeller to the stator to the turbine and thenback to the impeller

Cross-Section

of TorqueConverter


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VORTEX FLOW

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0

100

200

300

400

500

600

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

Engine RPM

Ft/LbsT

orque

0

0.5

1

1.5

2

2.5

3

TorqueMultiplicationRatio

Engine Torque Input Shaft Torque Torque Multiplication


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STATOR OPERATION

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STATOR OPERATION

As turbine (vehicle) speed increases and

approaches the speed of the impeller the turbinedischarge oil is accelerated to the point that itno longer strikes the front side of the statorblades, instead it strikes the backside of thestator blade causing the stator one-way clutch tounlock and the stator to freewheel

Since the stator is unlocked, fluid is not redirectedand no torque multiplication occurs

Fluid flow is rotary

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ROTARY FLOW

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As the speed of the turbine approaches thespeed of the impeller fluid flow switches fromvortex to rotary

After the fluid is discharged from the turbine it is

not redirected by the stator, instead it rotateswith torque converter Front-View of

Torque Converter


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ROTARY FLOW

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STATOR OPERATION

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FLOW DIRECTIONS

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CONVERTER PHASE TRADEOFFS

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STALL SPEED

Stall speed is the engine RPM at which the torque

converter has coupled enough that with the wheelslocked the engine is not able to increase RPM anyfurther

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TYPES OF STALL SPEEDS

Types of stall Speeds

True stallThis is the maximum rpm the engine can attain

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

Brake stall

This is the maximum rpm the engine can attainwith the brakes applied

The brakes generally will not have enough holdingpower to allow the engine to reach true stall speed

Flash stallThis is the rpm at which, when you accelerate at

full throttle from a dead stop the engine RPMflashesto TCIs recommended method of testingstall speed

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STALL TESTS

CAUTIONDo not brake stall a converter for

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

power developed by the engine isconverted in heat in the torqueconverter.

Wait at least 2 minutes betweenbrake stall tests

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FACRTORS AFFECTING STALL SPEEDS

Vehicle Weight

Vane/Fin Angle Horsepower Impeller to Turbine Clearance Camshaft Stator Design

Torque Rate Converter Diameter Gear Ratio

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VANE DESIGN

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Depending on the design and pitch of the blades,the impeller will scoop the most oil at a specificRPM, thus altering the stall speed

Hydrodynamic Drive Unit -2

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