ASE 251 Torque Converter Operation

ASE 251 Automatic Transmission/Transaxle Diagnosis and Service

ASE 251 Automatic Transmission/Transaxle Diagnosis and Service

Torque Converter FundamentalsJason DavesArapahoe Community College Automotive Technology Department1ASE 251 Arapahoe Community College Automotive Technology

This presentation should help to reinforce information from the text. The text for this course is Automatic Transmissions & Transaxles 4th Edition by Jack Erjavec, published by Thompson Delmar Learning 2007.1Lesson ObjectivesUpon completion of this presentation, you should be able to:Identify the major components of a torque converter and explain their purpose.Understand the fluid flows that occur in a torque converter.Discuss stator design and operation.Explain torque converter operation in the stall and coupling phases.Explain torque converter clutch design and operation.

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This slide presents the wanted outcomes of this lesson/presentation. In addition to quizzes and tests in this class, students will also be tested on this information during the ASE Automatic Transmissions Exam A2.2Torque Converter Assembly

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This is a picture of a complete torque converter assembly.3Torque Converter FunctionsThe torque converter supplies a fluid coupling between the transmission and the engine.It is similar to the clutch in a manual transmission or transaxle.It allows the engine to continue to run while the vehicle is stopped without killing the engineASE 251 Arapahoe Community College Automotive Technology4

A fluid coupling is a hydro-mechanical link. If you picture two fans facing each other with one fan turned on, you can imagine the air from one fan hitting the other fan and starting to drive the other fan in the opposite direction. This is how a fluid coupling works, except that fluid does not compress, and the fans are in an enclosed space, so the link is more stable.4Torque Converter FunctionsIt also multiplies torque at slower speeds to assist the engine in propelling the vehicle.With the addition of a torque converter clutch, the torque converter allows for a mechanical link between the engine and the transmission.The torque converter bolts to the flex plate and drives the transmission input shaft.ASE 251 Arapahoe Community College Automotive Technology

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Torque multiplication is when a small gear drives a big gear. As the small gear turns, the big gear turns more slowly, but the force exerted by the larger gear is increased. A torque converter works in much the same way. If the turbine is spinning more slowly than the impeller, then we have torque multiplication or gear reduction. 5Torque Converter ComponentsHousingThe torque converter housing holds all of the other components of the torque converter.

One end is bolted to the flex plate.

The other end is used to drive the transmission fluid pump.

The torque converter hub is machined to allow for a seal between the transmission oil pump and the hub.

It is usually made up of two pieces and welded together.

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This is a picture of a torque converter housing. A little known, but very helpful hint for technicians, is that when you bolt the torque converter to the flex plate, there is always one hole that is smaller and more square than the rest on a flex plate. That hole can be used to line up all of the other mounting holes, so that you dont have to tighten the bolts in as many stages.6Impeller

The impeller is driven by the engine, through the torque converter housing.

The impeller has many thin metal fins or blades similar to a fan.

These fins spins around in Automatic Transmission Fluid and force it away from the impeller like air from a fan.

Fluid from the impeller is directed to the blades of the turbine which is splined to the input shaft of the transmission.


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The impeller is like the fan that is turned on in the previous example.7Turbine

The turbine is splined to the input shaft of the transmission.

The turbine receives fluid directed from the impeller.

As the fluid hits the blades of the turbine, it forces the turbine to rotate.

The input shaft which is splined to the turbine, rotates at the same time.


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The turbine is like the fan that is turned off and being forced to spin by the fan that is turned on.8Stator

The stator is located between the impeller and the turbine.

The stator helps to redirect the fluid from the turbine back to the impeller so that the process can begin all over again.

The stator is mounted on a one way clutch, so that is cant fight the correct flow of fluid inside the converter.

The stator helps to achieve vortex flow of fluid inside the transmission which is where torque multiplication occurs.


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Vortex flow is created with the help of the stator and is the primary mechanism with which torque multiplication occurs. The flow of fluid begins with the impeller. Fluid from the impeller is directed towards the blades on the turbine. As fluid leaves the turbine and heads back to the impeller, it is moving a direction that fights the rotation of the impeller. The stator helps to redirect the fluid so that is hit the correct part of the impeller and helps it to increase momentum. This type of fluid flow inside the torque converter is called vortex flow. 9Torque Converter ClutchThe torque converter clutch forms a mechanical link between the transmission input shaft and the engine.

Fluid coupling from the converter is only about 90% efficient at best.

When the vehicle is at cruise and the torque converter is in coupling phase, there is an inherent 10% slip between the TC and the engine.

A TCC is inside the TC housing and can be forced against the housing to remove the 10% slip rate.


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The torque converter clutch is used to form a mechanical link between the engine transmission. It helps to eliminate the 10% inherent inefficiency in fluid coupling under cruise conditions.10Torque Converter StallTorque converter stall is when the impeller is spinning while the turbine is held stationary.Its good to have stall in the TCC because without it, your vehicle would die every time you came to a stop.Stall speed is the highest rpm the impeller can move before the turbine must move.


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Some torque converters in race applications can withstand really high stall speeds in 4500 rpm and up. This allows the engine to wind up just before the vehicle is launched. Stall speed for an average vehicle should be somewhere between 1200-1800.11Coupling PhaseWhen the speed of the turbine is nearly equal to the speed of the impeller The motion of the fluid during the coupling phase is called rotary flow.During rotary flow efficiency approaches 90% and slipping is held to a minimum.Arapahoe Community CollegeAutomotive Technology Department12

Coupling phase occurs when the vehicle is operating under cruise conditions. The fluid flow inside the converter switches from vortex flow to rotary flow.12Summary and Additional InformationTorque Converter operationTorque converter componentsFluid coupling and fluid flowTorque converter clutch operationAdditional InformationTorque Converter YoutubeTorque Converter Function Video

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We discussed basic functions of the torque converter which was to allow for a fluid coupling between the engine and transmission. We discussed the various components of the torque converter such as the housing, impeller, turbine, stator, and clutch. We discussed fluid coupling and various types of fluid flow inside the TC. Finally we discussed why a clutch is needed inside and torque converter and how it functions to improve vehicle efficiency. For additional information, check the following website(s). Thanks for listening.13SourcesErjavec, Jack. Automatic Transmissions and Transaxles 4th Edition. Thompson Delmar Learning. 2007http://www.youtube.com/watch?v=LEFWO3M4XOA. March 2010http://www.youtube.com/watch?v=MvLoX0z9qoY. March 2010

Thank you for watching.Arapahoe Community CollegeAutomotive Technology Department

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