AT131 Automatic Transmission I

Student Activities WEB  Copy

 

Course Syllabus

Lesson 1: Intro To Transmissions and Transaxles

Lesson 2: Planetary Gear Sets And Power Flow

Lesson 3: Hydraulic Basics

Lesson 4: Transmission Pumps

Lesson 5: Hydraulic Controls

Lesson 6: Apply Devices

Lesson 7: Torque Converters

Lesson 8: Automatic Transmission Fluids, Filters & Coolers

 

 

AT131 Automatic Transmission I

Spring 2003

Instructor: Darrell Hanan

Office:  Room 3101………………….Phone:441-4228

Office Hours:  3:00-4:00   Mon.-Fri.

E-mail:  dhanan@eicc.edu

Web:  http://faculty.eicc.edu/dhanan/

Text:  Automatic Transmissions and Transaxles 2nd Ed. By Birch & Rockwood

 

 

COURSE DESCRIPTION: This course is designed to provide basic knowledge in the diagnosis and repair of the automatic transmission. The student will develop skills necessary to perform in-car automatic transmission service. The student will also develop an understanding of the operation and service of torque converters, planetary gear trains and hydraulic components used in automatic transmissions. In-car service, as well as, removal-installation and overhaul procedures will be stressed in the lab portion of this course.

 

GENERAL COURSE GOALS:

In this course the student will develop skills necessary to perform in-car automatic transmission service. The student will also develop an understanding of the operation and service of torque converters, planetary gear trains and hydraulic components used in automatic transmissions. In-car service as well as Removal-installation and overhaul procedures will be stressed in the lab portion of this course.

 

POLICIES ON ACADEMIC DISHONESTY CAN BE FOUND IN THE EICCD STUDENT CODE OF CONDUCT PUBLISHED IN THE STUDENT HANDBOOK.

 

Final grade will be based on five areas:

Final Test...........……….......10%

Quiz scores..............…...…..25%

Lab Work Performance .......45%

Lab Log………………….…..10%

Employee Characteristics….10%

 

Final Grading Scale:

A > 90 - 100%

B > 80 - 89%

C > 70 - 79%

D > 60 - 69%

F > 59% or below

 

FINAL TEST: All students are required to take the comprehensive final test.

No unit tests will be given in this course.

 

Quizzes: A quiz may be given every other day. A missed quiz cannot be made up. Each student may be required to write 5 quiz questions as part of their quiz score. These are due before the quiz and will not be accepted late. The lowest quiz score will be dropped.

 

LAB WORK PERFORMANCE: Work performance will be evaluated based on weekly lab worksheets. Worksheets will be collected weekly as the work is completed. All worksheets must be turned in by Wednesday, March 17th.

 

LAB LOGS: A weekly lab log will be kept by each student.  The student will record his/her lab activity for the week.  A weekly grade will be determined from the students log.  The log must be turned in two school days after the last lab period for the week.  A log not turned in on time will result in a zero for the weekly lab grade.

The log entry must include the following: Name, Day & Date, Description of the lab activity for each day (minimum of five sentences), Five things learned that week, Difficulties experienced that week and Description of the best part of the lab activity for the week.

 

EMPLOYEE CHARACTERISTICS: Students will receive a weekly grade based on their demonstration of basic employee characteristics expected by employers. These include Dependability, Punctuality, Teamwork, Communication, Safety, and Cleanup. The instructor will rate each characteristic weekly on a scale

of 0 to 4:         0 - Unacceptable

                        1 - Occasionally meets minimum requirements

                        2 - Consistently meets minimum requirements

                        3 - Occasionally exceeds minimum requirements

                        4 - Consistently exceeds minimum requirements

 

 

COURSE COMPETENCIES/OUTCOMES:

Upon the completion of this course the student be able to;

 

·        Locate and interpret vehicle and major component identification numbers (VIN, vehicle certification labels, and calibration decals). P-1

·        Diagnose fluid usage, level, and condition concerns; determine necessary action. P-1

·        Diagnose transmission/transaxle gear reduction/multiplication concerns using driving, driven, and held member (power flow) principles. P-1

·        Inspect, adjust or replace throttle valve (TV) linkages or cables; manual shift linkages or cables; transmission range sensor; check gear select indicator (as applicable). P-1

·        Service transmission; perform visual inspection; replace fluids and filters. P-1

·        Inspect, adjust or replace (as applicable) vacuum modulator; inspect and repair or replace lines and hoses. P-3

·        Inspect, repair, and replace governor assembly. P-3

·        Inspect and replace external seals and gaskets. P-2

·        Inspect extension housing, bushings and seals; perform necessary action. P-3

·        Inspect, leak test, flush, and replace cooler, lines, and fittings. P-2

·        Inspect and replace speedometer drive gear, driven gear, vehicle speed sensor (VSS), and retainers.   P-2

·        Inspect, replace, and align powertrain mounts. P-2

·        Remove and reinstall transmission and torque converter (rear-wheel drive). P-2

·        Remove and reinstall transaxle and torque converter assembly. P-1

·        Disassemble, clean, and inspect transmission/transaxle. P-1

·        Inspect, measure, clean, and replace valve body (includes surfaces and bores, springs, valves, sleeves, retainers, brackets, check-balls, screens, spacers, and gaskets). P-2

·        Inspect servo bore, piston, seals, pin, spring, and retainers; determine necessary action. P-3

·        Inspect accumulator bore, piston, seals, spring, and retainer; determine necessary action. P-3

·        Assemble transmission/transaxle. P-1

·        Inspect converter flex plate, attaching parts, pilot, pump drive, and seal areas. P-2

·        Measure torque converter endplay and check for interference; check stator clutch. P-2

·        Inspect, measure, and reseal oil pump assembly and components. P-1

·        Measure endplay or preload; determine necessary action. P-1

·        Inspect, measure, and replace thrust washers and bearings. P-2

·        Inspect oil delivery seal rings, ring grooves, and sealing surface areas. P-2

·        Inspect bushings; determine necessary action. P-2

·        Inspect and measure planetary gear assembly (includes sun, ring gear, thrust washers, planetary gears, and carrier assembly); determine necessary action.  P-2

·        Inspect case bores, passages, bushings, vents, and mating surfaces; determine necessary action.    P-2

·        Inspect and reinstall parking pawl, shaft, spring, and retainer; determine necessary action. P-3

·        Inspect clutch drum, piston, check-balls, springs, retainers, seals, and friction and pressure plates; determine necessary action. P-2

·        Measure clutch pack clearance; determine necessary action. P-1

·        Air test operation of clutch and servo assemblies. P-1

·        Inspect roller and sprag clutch, races, rollers, sprags, springs, cages, and retainers; replace as needed. P-1

·        Inspect bands and drums; determine necessary action. P-2

 

            Note: P-1, P-2 & P-3 indicate the NATEF task priority level.

 

 

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AT131 Automatic Transmission I

Approximate Lesson Sequence

Reading Assignment Topics

 

Week              Discussion Topic                                                      Chapter; page

1          Into to Automatic Transmissions & Transaxles                  1; 1-30

2          Planetary Gear Operation And Power Flow                                  3; 51-96

3          Hydraulic Fundamentals                                                                   4; 97-121

4          Pumps & Control Devices                                                               5; 129-133,   

                                                                                                                            138-158    

            Apply Devices                                                                                   2; 31-50

                                   

5          Fluid Couplings & Torque Converters                                            7; 187-200

                                                                                                                        5:133-137

6          Transmission Fluids                                                             4; 123-128

7          Filters and Coolers                                                                           5; 137-138

8          FINAL EXAMS

 

 

AT131 Automatic Transmission I

Lab Assignments

q      RWD removal & installation

q      FWD removal and installation

q      Transmission fluid, filter change and band adjustment

q      RWD disassembly and reassembly

q      Shift linkage inspection and adjustment

q      Throttle valve linkage inspection and adjustment

q      Speedometer gear removal and installation

q      Governor removal, inspection and installation

q      Valve body and servo removal, inspection and installation

q      Transmission mount removal & installation

q      Vacuum modulator removal, inspection and installation

 

 

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Automatic Transmissions I

Lesson 1

Intro. To Transmissions and Transaxles

 

What components make up the vehicles drivetrain?

 

 

 

 

How does the engine create torque?

 

 

 

 

What is the function of the transmission?

 

 

 

 

What does the differential do?

 

 

 

 

What is the purpose of constant velocity joints?

 

 

 

What is torque?

 

 

 

What pushes the car forward?

 

 

Gear Train Theory

 

 

Underdrive –  torque multiplication and speed reduction

 

 

Overdrive – torque reduction and speed multiplication

 

 

Gear ratio –  factor of torque multiplication and speed reduction

 

 

Gear Ratio = Driven Gear Teeth

                      Drive Gear Teeth

 

Gear Ratio of multiple gear sets

 

Ratio of first x ratio of second

 

Final drive ratio = Transmission ratio x differential ratio

 

How does the final drive ratio affect vehicle acceleration and speed?

 

Engine torque = 200 ft-lbs.

Engine speed = 1800 rpm

Tire size = 36 in.

Differential ratio = 4:1

 

First gear ratio = 3:1

Second gear ratio = 1.5:1

Third gear ratio = 1:1

 

 

 

Automatic Transmission Basics

 

Transmission Gear Ranges

 

        Park – Neutral gear, output shaft locked by a parking pawl.

 

        Reverse – ratio about 1.8:1

       

        Neutral – neutral gear

 

        Overdrive – normal forward gear ranges, automatic shifting through all forward gears

 

        Drive – normal shifting without overdrive

 

                        See shift schedule – p. 270

       

        Manual Second – second only or 1-2 shift, used for engine braking

 

        Manual low – first gear only at start-up, may upshift to second, provides engine braking

 

                                Downshift to second if selected at high speed

 

 

 

 

 

 

 

 

 

 

 

Torque Converter

 

Fluid coupling that delivers engine power to the transmission.

 

        Components –

                Impeller or pump – connected to engine crankshaft

 

                Turbine – connected to transmission input shaft

               

 

                Stator – redirects flow of fluid from the turbine to the  impeller. Mounted on a one-way roller clutch.

 

        Function –

                - Automatically engage and disengage engine to transmission.

 

-         Absorb shock while changing gears

 

-         Multiples torque under load

 

 

Planetary gear set

 

        Compoments –

 

-         Sun gear

-         Planetary pinion gears and carrier

-         Internal ring gear

 

 

http://auto.howstuffworks.com/automatic-transmission2.htm

 

 

 

Function –

 

-         Provide underdrive, overdrive, direct drive and reverse   in one gear unit.

-         When one member is held torque and/ or direction is affected.

-         When two members are held direct drive is achieved.

 

 

What is the purpose of transmission fluid?

 

-         lubricate

-         cool

-         apply hydraulic force

-         transfer torque

 

 

Transmission Controls

 

Hydraulic – transmission fluid is controlled to apply a force which controls the action of the planetary gear set

 

Valves –

-         pressure regulating – controls transmission pressures

-         flow directing – feed pressure to the correct apply device (clutch, servo)

-         shift-point control – work together to determine shift- points

 

Electronic – TCM controls solenoids and force motors which affect the ATF flow to achieve better shift quality

 

 

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Automatic Transmissions I

Lesson 2

Planetary Gear Sets And Power Flow

 

Panetary gear set types

       

-         Simple

-         Simpson

-         Ravigneaux

 

        Simple –   One sun, one carrier, one ring gear: can provide underdrive (reduction), overdrive, direct drive, reverse or neutral.

                        See page 53.

 

Action

Ratio

Input

Held (reaction)

Output

U.D.

3.33:1

Sun

Ring

Carrier

U.D.

1.43:1

Ring

Sun

Carrier

O.D.

0.33:1

Carrier

Ring

Sun

O.D.

0.7:1

Carrier

Sun

Ring

R.-U.D.

2.33:1

Sun

Carrier

Ring

R.-O.D.

0.43:1

Ring

Carrier

Sun

Direct

1:1

Any two members locked together, no reaction

Neutral

NA

No member held

 

                       

        Simpson Gear Train

 

-         Two planetary gear sets with a common sun gear;

     consists of one sun, two planet carriers and two

     ring gears

-         Provides first and  second underdrive, direct drive

     and reverse.

 

Simpson Gear Train Ratios

Gear range

Ratio

Input

Held (reaction)

Output

First 

2.7:1

Front ring

Front carrier

Sun

 

 

Sun

Rear carrier

Rear ring

Second 

1.5:1

Front ring

Sun

Front carrier

Third

1:1

Front ring and sun

None

Front carrier

Reverse

1.9:1

Sun

Rear carrier

 Rear ring

 

 

Ravigneaux Gear Train

 

-         Provides underdrive, overdrive, direct and reverse

-         More compact than the Simpson gear train

-         Capable of more torque transfer

-         Three output members

 

Components

 

-         Large sun gear

-         Small  sun gear

-         Long pinion – engaged to large sun gear, short pinion and ring gear

-         Short pinion – engaged to small sun gear and long pinion

-         Planet carrier – holds both sets of pinions

-         Ring gear

 

 

 

http://auto.howstuffworks.com/automatic-transmission3.htm

 

 

          Ravigneaux Gear Ratios

Gear range

Ratio

Input

Held (reaction)

Output

Idler

Free

First 

2.4:1

Small sun

Carrier

Ring

Short

pinion

Large

sun

Second

1st stage 

2.2:1

Small sun

Large sun (ring)

Carrier

 

 

Second

2nd stage

0.67:1

Carrier

Large sun

Ring

Overall ratio

Is 1.47:1

Third

1:1

Large and small sun

Na

Ring

 

 

Fourth

0.67:1

Carrier

Large sun

Ring

 

Small sun

Reverse

2.0:1

Large sun

Carrier

Ring

 

Small sun

 

 

Transmission Bearings

 

Bearing – placed between two surfaces to reduce friction and wear.

 

        Types –

-         Sliding – soft material, usually bronze alloy, nylon, or plastic used for low load and slow rpm applications .

 

                - Bushing  - support a spinning component on a shaft       (radial load).

 

        - Thrust washer – space components along a shaft.  Controls end-play   (axial load).

 

- Roller – roller or balls which support the load.

                Components:  Inner race

                                       Rollers with cage

                                       Outer race

                - Bearing supports radial loads

                - Torrington bearing supports axial loads

 

 

 

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Automatic Transmissions I

Lesson 3

Hydraulic Basics

 

Hydraulics – using liquids under pressure to transmit motion and apply a force.

 

        -Liquids are practically incompressible.

 

Pascal’s Law – a confined fluid under pressure transmits the pressure equally in all directions.

 

The force a pressurized fluid applies is equal to the fluid’s pressure times the area the fluid is applied to.      F = P x A

 

The pressure in a fluid is equal to the force applied to the fluid divided by the area of fluid it is applied to.             P = F/A

 

As a pressurized fluid flows, pressure is lost in the fluid due to restrictions to flow.  The loss is called a pressure drop.  Pressure drop is determined by flow rate and amount of restriction. 

 

As a pressurized fluid flows, pressure is greater in the fluid before the restriction.  Pressure is lower in the fluid after the restriction.

Once flow stops pressure is the same on both sides of the restriction.

 

The pressure created in flowing fluid is determined by the capacity of the pump and the restriction to flow.

 

 

 

 

 

 

Automatic Transmission Seals

 

Classification of seals:

 

        Static – seals between two parts that do not move in relation to each other.

 

        Dynamic – seals between moving parts

                         (rotating or reciprocating)

 

        Positive – no leakage

 

        Non-positive – allows controlled leakage for lubrication purposes.

 

        Rubber seals – Positive seals

 

-         lathe cut – dynamic and axial movement

 

-         O-ring – static seal

 

-         Lip seal – dynamic and axial or rotational movement

 

-         may have a toroidial garder spring around the lip of a shaft seal.

 

Metal Sealing Rings – Non-positive seals

                                     Fit in a groove on a shaft

 

Types

-         Butt-end – ends touching when installed in the bore

-         Open-end – ends are gapped when installed in the bore

-         Hook-end – ends are locked together with small hooks on the end when installed.

Plastic Sealing Rings

 

Teflon – reduced wear on the sealing surfaces

 

        Scarf-cut – ends are cut at opposing angles

 

Vespel -

-          Solid one piece – must be sized to the correct O.D. with a sleeve tool before installing the bore.

 

 

 

 

 

 

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Automatic Transmissions I

Lesson 4

Transmission Pumps

 

What is the purpose of the transmission oil pump?

 

 

 

Types –

-         Crescent Gear –

        - small external gear

        - large internal gear

        - a crescent in the pump body separates the gears on one half.

 

-         Rotor or gerotor – similar to a crescent gear pump without the crescent.  The rotors have rounded lobes in place of gear teeth.

 

Fixed displacement pumps – These pumps’ volume output depend on speed.  Each revolution produces a fixed amount of flow volume.  A pressure regulator dumps excess flow to maintain the correct pressure at all speeds.  These pumps are not energy efficient.  Gear and rotor pumps are fixed displacement pumps.

 

Vane – Vanes contained in a rotor are carried around inside a circular slide as the rotor spins.  The fluid is carried between the vanes as they move around the slide.  These pumps have a variable displacement. The output volume is varied by repositioning the slide with hydraulic pressure.  These pumps are more efficient.  They only pump what is required.

 

 

 

 

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Automatic Transmissions I

Lesson 5

Hydraulic Controls

 

What are used to control hydraulic pressure and flow direction?

 

 

 

 

Types of Valves

 

-         Check valve – allows fluid flow in only one direction

        -Types –

                - Ball – steel or rubber ball

                                - seats in a small opening when a small back flow occurs.

 

- Poppet – small metal disk or block that is held closed with a spring.  The spring closes the valve without back flow.  Check balls may       have a return spring.

 

-         Spool valve – used to direct fluid flow.

        -a solid metal cylinder which is narrowed in the center, which is placed in a bore.

 

 

 

 

 

The lands open and close passages in the sides of the bore as it moves.  The valve is moved by mechanical or hydraulic forces on the reaction areas of the spool.  Spool valves are used as control valves that direct pressure to hydraulic actuators.

-         Relief valve – used to limit maximum pressure.

        -A spool valve with a calibrated spring on one reaction area and pump output acting on the other reaction area.

           When pump pressure exceeds the force of the spring, the valve moves and exhausts excess flow to relieve the pressure.

 

-         Pressure Regulating Valve – a valve that varies outlet pressure.

         -A spool or ball valve that reacts to changes in mechanical or hydraulic forces to vary the amount of fluid that is exhausted. 

          -As the exhaust flow varies, the outlet pressure varies.

        - If exhaust flow increases, outlet pressure decreases.

-Other Controls

        - Orifice – An orifice is a calibrated restriction in a fluid passage that causes a reduction in pressure and    flow. 

Used to control the speed of hydraulic application and release of actuators.

 

 

 

 

 Valve Bodies

 

A valve body contains bores, spool and check valves, balls, springs and fluid passages that make up the hydraulic control unit for the transmission.

 

Components –

               

 - Valve body

 

                -  Separator plate – located between the valve body        and transmission case.  The separator plate controls flow from the valve body to

 the transmission using orifices, check balls, and restrictions.  It also prevents cross flow between                            passages in the transmission case and valve body        (worm tracks).

 

 

Transmission Pressures

 

Mainline pressure

-         Limited by engine speed and pressure regulator valve

-         Applies clutches and bands

-         Lubricates components

-         Fills the torque converter with low pressure fluid

-         Supplies fluid to the governor and throttle pressure circuits.

-         75 to 200 psi

 

 

 

 

 

 

        Throttle Pressure (TV pressure)

 

-         Signals engine load

-         Sensed and controlled by linkage to the engine throttle, vacuum modulator, a combination of the two or electronic sensors (TPS, MAP).

-         Throttle pressure is modified line pressure.

-         Greater engine load results in higher TV pressure

-         Throttle pressure affects line pressure.  As throttle pressure increases, line pressure increases.

 

        Governor Pressure

-         Signals vehicle speed.

-         Sensed and controlled by a governor driven by the transmission output shaft.

-         Governor pressure is  modified line pressure

-         Higher vehicle speed results in higher governor pressure.

 

TV pressure and governor pressure are signal pressures which control shift valves.  They act on opposite ends of the shift valve spool.

 

        Boost Pressure

-         Increased mainline pressure.

-         Needed for better holding force under heavy load.

-         Reverse, manual low.

-         Line pressure is boosted by throttle pressure applied to the pressure regulator valve.

       

 

 

               

 

Shift-point Control Valves

 

Transmission shifts are affected by engine torque load and vehicle road speed.

 

Governor Valve - senses vehicle road speed

 

Governors may be gear driven by the output shaft or mounted on the output shaft.

 

All governors use two sets of flyweights and springs. Centrifugal force causes the flyweights to move out. Spring force cause the weights to move back.

 

 Electronically shifted transmissions use a Vehicle Speed Sensor to determine road speed.

 

Throttle Valve and Modulator Valve – sense engine torque load

 

        Throttle Valve

-         moved by a rod or cable connected to the engine throttle

-         increases throttle pressure as the engine throttle opens

-         increases main line pressure based on throttle pressure

-         cable or rod must be adjusted

 

 

 

 

 

 

 

 

        Modulator Valve

-         diaphragm acted on by intake manifold vacuum moves the modulator valve

-         increases modulator pressure as the engine vacuum decreases

-         increases main line pressure based on modulator pressure

-         modulators may have an adjustment screw in the vacuum port

 

 

Throttle pressure and modulator pressure are engine torque load inputs to the transmission.

 

Electronically shifted transmissions sense engine torque load with a MAP or TPS.

 

 

 

 

 

 

 

 

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Automatic Transmissions I

Lesson 6

Apply Devices

 

Servo and Band

 

-Servo

        - piston moved by hydraulic pressure

        - returned by a spring or spring and hydraulic pressure

        - some servo apply pins are different lengths for adjustment

 

- Band

-         steel or cast iron lined with friction material

-         wraps around the outside of a drum to hold it from rotating

-         one end is moved by the servo, one end held against the transmission case.

 

                -Types

                        - single wrap – one piece thin steel

                        - double wrap – cast iron band that is split with overlapping ends.

 

Bands need to be adjusted for proper fit around the drum.  Too much clearance and the band will slip, too little clearance and the band will overheat.                

Some band anchor points are adjustable externally.

 

 

 

 

 

 

Multiple Disc Clutch

       

        Components –

-         Clutch piston, installed in a drum or the case or pump.

-         Return spring

        - multiple coil springs

        - single large coil spring

        - Belleville (diaphragm) spring acts as a force multiplier and return spring.

- Friction discs or plates – steel discs covered on both sides with friction material. 

        - Steel discs – smooth steel discs

        - Pressure plate – heavy steel disc used on one or both ends of the clutch stack.

 

 

The steel discs and friction discs are stacked alternately and splined opposite of each other; one is internal and one is external.  The pressure plate is splined the same as the steel discs.

 

Clutch packs must have clearance when assembled to allow free-wheeling of planetary members.

 

Clutch pack clearance is adjusted in a variety of ways.

-         different pressure plate thicknesses.

-         different snap ring thicknesses.

-         different steel disc thicknesses.

 

Some clutch packs have a single wave plate or wave steel disc to cushion clutch application.

 

 

 

 

One-Way Clutches – allows rotation in one direction only.

        Types –

-         Roller

        - round race

        - cam race

        - rollers and springs – thins wave steel

Rollers are locked by the cam in one rotational direction

 

-         Sprag

        -  two round races

        -  figure eight shaped steel sprags and springs

        - sprags lock races together in one rotational direction.

 

Accumulators

 

        Purpose – slow the build up of hydraulic pressure to soften a shift.

 

        Components – cylinder, piston and spring.

 

 

Diagram:

 

 

 

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Automatic Transmissions I

Lesson 7

Torque Converters

 

Torque converter -

A fluid coupling that transmits engine torque to the transmission without a direct mechanical connection.

 

http://auto.howstuffworks.com/torque-converter2.htm

 

Components and Operation

-         Cover with impeller – turned by crankshaft.  Impeller causes the ATF to rotate. Sometimes called the pump.

- fins curved in the direction of rotation.

-         Turbine – moved by the ATF’s energy

        -connected to the transmission input shaft.

        - fins curved opposite the direction of rotation.

 

-         Stator with over-running clutch

1.       Re-directs ATF flow from the turbine back to the impeller.

2.       Changes the direction of the ATF as it leaves the turbine and re-enters the impeller.

3.       Increases the ATF’s energy and provides for torque multiplication.

4.       Does not turn when the turbine speed is less than 90% of the impeller speed (torque multiplication).

5.       Rotates with the impeller and turbine when the turbine speed is 90% of impeller speed (coupling phase).

 

ATF flows in two ways inside the converter.

 

Rotary Flow - flow in the direction of impeller rotation.  Occurs mainly during the coupling phase.

Vortex Flow – a circular flow from the impeller to the turbine, back to the impeller.  Occurs mainly during torque multiplication.

 

Both types of flow can occur at the same time.  Flow shifts from vortex to rotary as the speeds of the turbine and impeller equalize.  

 

The stator redirects the vortex flow so the ATF does not work against the impeller as it leaves the turbine. 

 

The impeller and turbine are fitted with guide rings to smooth the vortex flow. 

 

Torque Multiplication

 

Torque multiplication occurs when the stator redirects the vortex flow.  The impeller increases the speed of the vortex flow.  The ATF’s energy increases and pushes harder on the turbine blades, increasing torque. The higher the vortex velocity, the greater the torque multiplication.

 

This occurs when the impeller speed is high and the turbine speed is low.  Impeller speed is typically twice that of the turbine at maximum torque multiplication. 

 

Converter stall speed – the fastest speed the engine can reach while the turbine is not spinning.

 

Large diameter converters have a low stall speed because the fluid is moving faster around the edge of the converter.  Used with higher HP engines. 

-         Less torque multiplication, but couple well at high speeds

-         Efficient

 

 

Small diameter converters have high stall speeds.  Used with low HP engines. 

-         High torque multiplication at high engine speed.

-         Do not couple well, not fuel efficient.

 

Vane pitch affects torque multiplication and coupling speeds.

 

During torque multiplication the converter generates heat that must be removed to prevent damage.

 

Lock-up Converters

 

A lock-up converter uses a clutch to connect the turbine directly to the impeller, near coupling speed, to increase fuel efficiency.

 

Types-

        - Hydraulic – uses hydraulic pressure to apply the clutch.

                                        - Lock up is controlled by an electric        solenoid.

 

Lockup conditions are:

 

-         engine load

-         vehicle speed

-         engine temperature

-         brakes not applied

-         throttle movement

-         transmission gear

 

Dampener springs in the clutch soften the engagement. 

 

               

        - Centrifugal – Locks up based on turbine speed only.  The centrifugal clutch is splined to the turbine as the speed increases the clutch shoes fly out  and engage the impeller housing.  The clutch may have slippage at lower speeds.

 

- Viscous – similar to hydraulic lock-up

-         a viscous clutch, similar to a cooling fan clutch connects the lock-up clutch to the turbine.

-         Silicone fluid transfers torque in the viscous clutch.

-         Slips 40-60 rpm when locked.

-         Smooths clutch application.

 

 

 

 

 

 

 

 

 

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Automatic Transmissions I

Lesson 8

Automatic Transmission Fluids, Filters & Coolers

 

Types of fluid

 

Non-modified –

-         Static co-efficient of friction higher than dynamic co-efficient of friction.

-         Friction force increases as the friction material locks up.

-         Firm shift, high application pressure needed to prevent slipping.

 

Friction-modified –

-         Static co-efficient of friction much lower than dynamic co-efficient of friction.

-         Friction area is greater on clutches and bands.

-         Smooth, softer shifts.

 

 

10-15% of ATF is additives.  See page 124 and 126.

 

http://www.niehoff.com/techtips/trans.html

ATF Filters

 

Surface filters

-         Screen – wire or nylon mesh, not prone to clogging.

-         Paper – cellulose or Dacron synthetic fabric.

-clogs easily, most have a bypass valve.

 

 

Depth filters

-         Felt – polyester, filters most particles, not likely to clog. 

 

 

Transmission coolers

 

-         Coolers are located in the radiator tank.

-         ATF flows from converter to cooler to lube circuit.

-         Auxiliary coolers are used for towing applications.

 

 

 

Basic transmission inspection

- Fluid level

-         will be just at ”add” line when cold, will expand when hot.

-         Low level will cause problems.

-         Level too high will cause foaming or aeration. 

                                                         

-Fluid color and odor

        - look for signs of overheating

-         look for signs of contamination:  milky

 

 

 

 

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