4.8 GRX Auto - Torque Converter Lockup

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Abri Hoffman
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4.8 GRX Auto - Torque Converter Lockup

Post by Abri Hoffman » 13 Sep 2009 20:29

Can anybody tell me how noticeable the torque converter lockup on the 4.8 auto is.
During our trip to Kaokoland we had a discussion on the difference between the Patrol and Cruiser autobox. In the Cruiser the lock-up is very noticeable whereas in the Patrol hard to detect.
Would be interesting to hear other 4.8 drivers observation of this.
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Patrol4.8 » 14 Sep 2009 10:48

:think: Wat is torque converter lockup? :redface:
Jammer ek weet nie, verduidelik asb Abri :salute:
Cornelius Kotzé
'03 Patrol GRX 4.8 AT
OME 2" lift
33" BFG A/T

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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Abri Hoffman » 14 Sep 2009 11:32

Cornelius, eerder as wat ek probeer verduidelik lees hierdie:
http://dnr.louisiana.gov/sec/execdiv/te ... to/f/f.htm

En hierdie uit die manual:

Lock-Up Control
Lock-up control means that torque converter sliding is eliminated and coupling the lock-up piston in the torque
converter raises the power transmission efficiency.
The lock-up solenoid is controlled by a signal from the TCM, the lock-up control valve operation is controlled,
and the torque converter lock-up piston is coupled or released.

TORQUE CONVERTER CLUTCH CONTROL VALVE CONTROL
I The circuit that supplies operating oil pressure to the lock-up piston chamber is connected to the lock-up
control valve. This valve is switched by the lock-up solenoid with signals from the TCM.
I In this way, the circuit that supplies operating oil pressure to the lock-up piston chamber is controlled to
the released side or the coupled side.

Lock-Up Released
I In the lock-up released state, the lock-up control valve is set into the un-locked state by the lock-up solenoid
and the lock-up apply pressure is drained.
In this way, the lock-up piston is not coupled.

Lock-Up Applied
I In the lock-up coupled state, the lock-up control valve is set into the locked state by the lock-up solenoid
and lock-up apply pressure is generated.
In this way, the lock-up piston is pressed and coupled.

SMOOTH LOCK-UP CONTROL
When shifting from the lock-up release state to the lock-up coupled state, the current output to the lock-up
solenoid is controlled with the TCM. In this way, when shifting to the lock-up coupled state, the lock-up clutch
is temporarily set to the half-clutched state to reduce the shock.

Half Clutched State
I The current output from the TCM to the lock-up solenoid is varied to steadily increase the lock-up solenoid
pressure.
In this way, the lock-up apply pressure steadily rises and while the lock-up piston is put into half-clutched
status, the force pressing on the lock-up piston is increased and the coupling is completed smoothly.
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Gerrit Loubser » 14 Sep 2009 11:34

The torque converter is a type of fluid coupling in between the engine and transmission. It works a bit like a close-coupled hydrodynamic pump and motor. Inside the torque converter there is an impeller (driven by the engine), which imparts motion to the transmission fluid inside. This transmission fluid is then redirected onto the turbine by stator vanes, where the fluid imparts energy to the turbine vanes. This results in the generation of torque. Due to the hydrodynamic nature of torque converter operation and due to the presence of the stator vanes that redirect flow, the torque converter output torque can be higher than engine output torque, which means that the vehicle can be very flexible in operation, even with very tall overall gearing.

The end result is that drive torque is transferred to the transmission, while allowing the vehicle to pull away from a standing start. In order to do this, there must be "slip" in the torque converter, i.e. it must be possible for the engine to be spinning while the transmission is spinning at a slower speed or is even stationary. This slip results in energy loss (some of the mechanical energy that the engine inputs into the torque converter is converted to heat), which is the reason why automatic versions of vehicles typically are a little less fuel efficient than their manual counterparts. Slip losses are greatest when the speed difference between the engine and transmission are greatest, reaching a maximum at torque converter stall where the transmission is stationary while the engine is spinning. In this latter situation, all energy is dissipated as heat. At cruise, the engine speed is only a little higher than the transmission speed, but there still has to be slip (and energy losses). Maximum torque multiplication occurs at torque converter stall (in the case of the RE5R05A transmission used in the Patrol 4.8 Auto, the stall torque multiplication ratio is 2).

In order to reduce the slip losses at cruise, the manufacturers have added a lock-up clutch that locks the input and output shafts of the torque converter together. When the torque converter is locked, the vehicle is effectively directly driven; the torque converter is elliminated from the drivetrain. This mode of torque transmission is referred to as torque converter lock-up mode or just lock-up mode. When the torque converter is unlocked, the torque converter works as outlined in the previous paragraph above. This mode of torque transmission is referred to as torque converter mode.

Now the amount of torque that can be transferred and the amount of heat that can be dissipated by the lock-up clutch are both limited (the lock-up clutch is not very large, being packaged in an area where real estate is at a high premium). This means that the lock-up clutch can only be activated in a limited regime of vehicle operation (normally at part throttle in cruise mode only). Lock-up occurs under the command of an electronic control unit that senses vehicle speed, engine speed, transmission fluid temperature and input torque and bases its decisions on electronic engine and transmission maps stored in its memory. The Patrol 4.8 only locks the torque converter in 5th gear if the transmission is left in D and 4th gear if the transmission is in "Triptronic" mode.

The Patrol has special smooth lock-up control functionality to mask the transition from unlocked to locked. What it does is to vary the lock-up pressure steadily and gradually until 100% lock-up is achieved (a bit like modulating the clutch in a manual vehicle to achieve smooth gear changes).

P.S. I was too slow and Abri posted while I was typing...
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Abri Hoffman » 14 Sep 2009 11:36

O ja, die gesprek.

Op die Cruiser is daar in 5de 'n punt bo 80km/h wat dit kompleet lyk of die kar in "overdrive" gaan. Die revs val met so 300 - 400revs. Dit is wanneer die torque converter lock. Ons kon nie enigiets soortgelyks in die Patrol sien nie en die verduideliking in die manual verduidelik dalk die rede daarvoor. Die enigste probleem is jy weet nie of die torque converter werk soos bedoel nie.
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Gerrit Loubser » 14 Sep 2009 11:56

Abri, one can determine whether the lock-up function is working by checking what the engine speed is at a given road speed and comparing that to the theoretical value.

I did a very hasty calc (please don't crucify me if I made a boo-boo) for the 4.8 Patrol on standard tyres and it looks like the engine should be spinning at about 2375 rpm at a true speed of 120 km/h (or 2400 rpm at 121 km/h). If it is spinning faster then the lock-up clutch is not engaged.
Gerrit Loubser

2003 Land Cruiser 100 VX TD
1999 Patrol 4.5E GRX M/T ("Imvubu") - GONE; Go well Old Girl :-(
2003 Pajero 3.2 DiD LWB A/T - GONE; One of the best cars I ever had :-(
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Patrol4.8 » 14 Sep 2009 12:21

Ek is ongelukkig nie so tegnies ingestel soos julle ouens nie.
As ek teen 'n konstante snelheid ry en die versneller liggies trap, dan klim die revolusies onmiddellik met omternt 200rpm.
Cornelius Kotzé
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OME 2" lift
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Abri Hoffman » 14 Sep 2009 12:26

Thanks Gerrit, this is exactly what I was looking for.
This is on Bredell's 4.8. Just spoke to him, they replaced the lock-up solenoid last week after some problems he had after our Kaokoland trip.

First long trip (150km) to Port Owen the car was sitting at 2700rpm at 120km/h.
Coming back the car was sitting at 2400rpm at 120km/h.

The consumption is still at only 4.4km/l though. Conditions are the same there and back, other than that the there trip was from 350m above see level to sea level.

Is it possible that if the lock-up never worked and got fixed that it did not lock up on the trip to Port Owen but started working on the trip back?

Consumption still seems very high at 120km/h.
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Abri Hoffman » 14 Sep 2009 12:27

Cornelius, dis presies waarvoor ek soek. Dit se vir my jou lockup werk en ontkoppel die oomblik wat jy krag gee in lyn met wat die manual beskryf.
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Re: 4.8 GRX Auto - Torque Converter Lockup

Post by Patrol4.8 » 14 Sep 2009 12:39

Jy het genoem dat Bredell 4.4 km/l kry, is dit met of sonder sleepwa?
Ek het my sleepwa 6200km deur Nam gesleep en my gem verbruik was 4.4km/l :redface:
Ek gaan woensdag of donderdag ff uilaat opsit en dan die chip ook doen, hopelik verberter die verbruik :pray:

Groete
Cornelius Kotzé
'03 Patrol GRX 4.8 AT
OME 2" lift
33" BFG A/T

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