Torque Converter lock-up function
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By Gregg Nader T ypical lock-up torque converters have two oil circuits to keep the converter charged with oil and to control release/apply of the torque converter clutch. Some Ford torque converters are different, having an additional third oil circuit in the torque converter. In most conventional non lock-up torque convert- ers, oil is fed to the rear half of the torque converter (converter impeller) and then flows through the front half of the converter (converter turbine) and exits. The direction of the oil flow never changes. In a typical lock-up torque converter, the direction of oil flow into and out of the torque converter changes direction to control release/apply of the torque converter clutch. From the moment the engine is started, oil is fed between the torque con- verter front cover and the lock-up piston. This keeps the TCC piston pushed away from the front cover and in the TCC released position. Oil then flows through the rear half of the converter and exits. Figure 1 shows a typical torque converter in TCC released mode. To apply the torque converter clutch the TCC apply/switch valve changes position and the direc- tion of oil flow through the converter is reversed. Fluid under pressure in the impeller and turbine area (TCC apply pressure) pushes the TCC piston into the front cover engaging the converter clutch. TCC does not fully apply until the oil that was between the front cover and the lock-up piston (TCC release oil) is allowed to exhaust. The rate of TCC engagement is affected by two factors. How much apply pressure is pushing the TCC piston towards the cover, and orifices that con- trol how fast the release oil exhausts. Apply pressure and release oil exhaust rate can be varied, so lock-up has three stages: full release, controlled modulated apply and full apply. Figure 2 shows a typical torque converter in TCC applied mode. Ford CD4E, AXOD/E, AX4N, AODE/4R70W and G4/F4EAT transmissions use three oil circuits to keep the converter charged with oil and to control the release/apply of the torque converter clutch. Oil flows into the rear of the torque converter (convert- er impeller CI), then flows through the converter turbine (CT) and exits. Oil flow in the CI and CT ©2003 Sonnax 98 sonnax ® 800/843-2600 • 802/463-9722 • fax: 802/463-4059 • www.sonnax.com • [email protected] Typical TCC On Exhaust TCC Apply Oil Front Cover TCC Piston Applied Converter Charge To Cooler From TCC Solenoid TCC Apply/Switch Valve Typical TCC Off TCC Release TCC Apply/Switch Valve Converter Charge Converter out to cooler From TCC Solenoid TCC Piston Released Front Cover Figure 1 Figure 2
description
Understand what the lock-up functio
Transcript of Torque Converter lock-up function
By Gregg Nader
T ypical lock-up torque converters have two oilcircuits to keep the converter charged with oiland to control release/apply of the torque
converter clutch. Some Ford torque converters aredifferent, having an additional third oil circuit in thetorque converter.
In most conventional non lock-up torque convert-ers, oil is fed to the rear half of the torque converter(converter impeller) and then flows through thefront half of the converter (converter turbine) andexits. The direction of the oil flow never changes.
In a typical lock-up torque converter, the directionof oil flow into and out of the torque converterchanges direction to control release/apply of thetorque converter clutch. From the moment theengine is started, oil is fed between the torque con-verter front cover and the lock-up piston. This keepsthe TCC piston pushed away from the front coverand in the TCC released position. Oil then flowsthrough the rear half of the converter and exits.Figure 1 shows a typical torque converter in TCCreleased mode.
To apply the torque converter clutch the TCCapply/switch valve changes position and the direc-tion of oil flow through the converter is reversed.Fluid under pressure in the impeller and turbine area(TCC apply pressure) pushes the TCC piston intothe front cover engaging the converter clutch. TCCdoes not fully apply until the oil that was between thefront cover and the lock-up piston (TCC release oil)is allowed to exhaust.
The rate of TCC engagement is affected by two factors. How much apply pressure is pushing theTCC piston towards the cover, and orifices that con-trol how fast the release oil exhausts. Apply pressureand release oil exhaust rate can be varied, so lock-uphas three stages: full release, controlled modulatedapply and full apply. Figure 2 shows a typical torqueconverter in TCC applied mode.
Ford CD4E, AXOD/E, AX4N, AODE/4R70Wand G4/F4EAT transmissions use three oil circuitsto keep the converter charged with oil and to controlthe release/apply of the torque converter clutch. Oilflows into the rear of the torque converter (convert-er impeller CI), then flows through the converterturbine (CT) and exits. Oil flow in the CI and CT
©2003 Sonnax
98 sonnax® 800/843-2600 • 802/463-9722 • fax: 802/463-4059 • www.sonnax.com • [email protected]
Typical TCC On
Exhaust
TCC Apply Oil
FrontCover
TCC Piston Applied
ConverterCharge
To Cooler
FromTCC Solenoid
TCC Apply/Switch
Valve
Typical TCC Off
TCC Release
TCC Apply/Switch
Valve
ConverterCharge
Converter out to cooler
FromTCC Solenoid
TCC Piston Released
FrontCover
Figure 1
Figure 2
circuits is the same as a non lock-up con-verter, the direction of oil flow throughthese circuits never changes. The 3rd oil circuitis called Converter Bypass or CBY and controlsapply/release of the converter clutch.
From the moment the engine is first started,oil is fed into the converter through both CI(converter impeller) and the CBY bypass oilcircuits. Oil exits the converter through theCT (converter turbine) oil circuit. Bypass oilflows between the torque converter frontcover and the lock-up piston. This keeps theTCC piston pushed away from the frontcover in the TCC released position. Figure 3shows a typical Ford bypass torque converterin the TCC released mode.
To apply the torque converter clutch, thePCM controls the TCC solenoid to changethe position of the bypass valve and reducesCBY pressure. As the bypass valve moves, itrestricts oil into the bypass circuit andremaining oil pressure between the frontcover and TCC piston is allowed to exhaust.CBY oil pressure can be varied so lock-uphas three stages, full release, controlledmodulated apply and full apply. Figure 4shows a typical Ford bypass converter in theTCC applied mode.
Problems with Bypass Circuits:Low converter pressure (CT) is the equiva-lent of low TCC apply pressure and results inTCC slip. Low converter pressure can becaused by a reduced volume of oil being fedto the converter due to problems in the valvebody, pump, torque converter as well asexternal electronic controls.
Valve body bore wear at the bypasssleeve/plunger, bypass valve, and converterregulator valves result in lower overallCT/TCC apply pressure and limits thebypass valves ability to control CBY by-pass oil.
High CT pressure from a stuck converterregulator valve or high line pressure cancrack a TCC piston and result in a TCC slip code.
Valve body pressure regulator bore wearas well as trouble codes, FMEM (PCM fail-ure mode) can also result in lower converter pressure. Low pump volume orhigh line pressure causes the pressure regula-tor valve to restrict converter charge (CI).
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Bypass ConverterTCC Off
TCC ReleaseCBY
CBY Exhaust
ConverterCharge CI
Converter out to cooler CT
FromTCC Solenoid
CT
CI
Bypass Valve
Bypass Sleeve and Plunger
TCC Piston Released
FrontCover
Bypass ConverterTCC On
TCC ReleaseCBY
CBY Exhaust
ConverterCharge CI
Converter out to cooler CT
FromTCC Solenoid
TCC Piston Applied
Bypass Sleeve and Plunger
Bypass Valve
CI
CT
FrontCover
Figure 4
Figure 3
