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Toyota 4WD review (1)

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Eugenio,77
mail@toyota-club.net

© Toyota-Club.Net
Feb 2004 - Nov 2015


Part 1. Initially FF models with automatic transmissions
Part 2. Initially FR models with automatic transmissions

1.1. STD I type
Full-time four wheel drive, with a symmetrical center differential, locking by hydromechanical clutch

The good old full-time, used for initially FF models, was really "full" and "permanent", with three differentials (center, front, rear) and symmetrical 50:50 torque distribution between the front and rear wheels.

Corolla (90..110), Corona (190..210), Vista-Camry (20..40), RAV4 (10) families was applied with multi-plate hydromechanical clutch for center differential locking.


Pressing "C.DIFF AUTO" button permits control unit to select the locking rate depending on the driving conditions, when button is not pressed center differential continuously free. As A241H gearbox based on gearbox with simple hydraulic control, its locking principles are less progressive (detailed description - "A241H automatic transmission"), whereas A540H has реализовано real electronic control with feedback (detailed description - "A540H automatic transmission").

Stananrd for everyday driving is the automatic mode, so disabling it is provided only for towing or using the undersized spare wheel. The maximum locking rate is realized at selector lever position "L" and "R" (manual).

Since 1994 models with A540H had not "C.DIFF AUTO" button - the driver is completely removed from the locking control and automatic mode activated permanently.

It should be noted that STD I is the most advanced, reliable and efficient among all the variations of Toyota all-wheel drive for initially FF cars. Unfortunately, no such models were produced since 2002.

ModelProductionTransmissionDifferential locking
Caldina 1901992-2002A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina 1901992-1996A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina 2101996-08.1998A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina ED 2001993-1998A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corolla / Sprinter 901987-1992A241Hcenter - hydromechanical clutch
Corolla / Sprinter 1001992-2002A241Hcenter - hydromechanical clutch
Corolla / Sprinter 1101995-2000A241Hcenter - hydromechanical clutch
Corolla Spacio 1101997-2002A241Hcenter - hydromechanical clutch
Corona 1901992-1996A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corona 2101996-12.1997A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corona Exiv 2001993-1998A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Ipsum 101996-04.1998A540H+AF2BEcenter - electronically controlled hydromechanical clutch
RAV4 101994-2000A540H+AF2BEcenter - electronically controlled hydromechanical clutch, rear - Torsen (opt.)
Sprinter Carib 951988-1995A241Hcenter - hydromechanical clutch
Sprinter Carib 1101995-2002A241Hcenter - hydromechanical clutch
Vista / Camry 201988-1990A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Vista / Camry 301990-1994A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Vista / Camry 401994-1998A540H+AF2BEcenter - electronically controlled hydromechanical clutch


1.2. STD II type
Full-time four wheel drive, with a symmetrical center differential, locking by viscous coupling

At the second half of 1990s Toyota turned to new transmission types and more primitive solutions, so STD II obtained viscous coupling for the center differential locking. Design simplifying did not improve the reliability, but greatly worsened performance - due to too low viscous coupling efficiency compared to hydromechanical.

Combined front and center differentials with viscous coupling was used by Toyota previously - at models with manual gearbox. New scheme follows the same principle, only visible difference is five instead of four satellites in center differential.

The rear differential could be either free/open, or LSD Torsen (option).

Note. In technical English all "self-locking"/"limited slip differentials" called "LSD". However, they are divided into viscous (with "closed" viscous coupling filled with silicone liquid), friction (the disks and plates operates in differential fluid), Torsen etc.

ModelProductionTransmissionDifferential locking
Alphard 102002-2008U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Caldina 215W GTT1997-2002U140F+MF2AVcenter - viscous coupling
Caldina 246 GT42002-2007U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Harrier 101997-2003U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Harrier ACU35/GSU3#2003-2013U140F+MF2AV
U151F+MF2AV
center - viscous coupling, rear - Torsen (opt.)
Highlander 202000-2003U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Kluger2000-2007U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Lexus RX MCU3#1998-2003U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Lexus RX350 GSU3#2006-2008U151F+MF2AVcenter - viscous coupling
RAV4 202000-2006U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)


1.3. V-Flex type
Basic front-wheel drive, no center differential, the rear wheels are connected via viscous coupling


Since 1997 many Toyota's models obtain the new four-wheel drive known as "V-Flex Fulltime 4WD". It's not true "fulltime" - actuallly it is just auto-connected rear axle (rear wheels). Center differential was eliminated, and the torque through transfer (or, simply, bevel gearbox) is drive by propeller shaft to back. Before the rear differential the viscous coupling mounted, which connects the propeller shaft and the input shaft of rear differential only when front wheels slipping (V-Flex II). In the other cases the car remains front-wheel-drive.

B-class models (Starlet, Tercel, first Vitz families) had the such scheme of simplified all-wheel drive previously (since 1990), the main difference - viscous coupling not installed on the rear axle but connects the two parts of the propeller shaft (V-Flex I).

Scheme imperfections:
- viscous coupling tardy "triggering"
- full locking inability
- potential danger when aggressive driving
- low durability and reliability of the viscous coupling

ModelProductionTransmission
V-Flex I
bB 302000-2005U340F
Funcargo1999-2005U340F
Ist 602002-2007U340F
Platz1999-2005U340F
Porte 102004-2012U340F
Probox / Succeed 502002-2014U340F
Probox / Succeed 1602014-..K310F
Raum 101997-2003A244F+CF1A
Raum 202003-2011U340F
Starlet 801989-1996A244F+CF1A
Starlet 901996-1999A244F+CF1A
Tercel / Corsa / Corolla II 401990-1994A244F+CF1A
Tercel / Corsa / Corolla II 501994-1999A244F+CF1A
Vitz 101999-2005U340F+MF1A
Will Cypha2002-2005U340F
V-Flex II
Avensis 2502003-2008A248F
bB 202006-..-
Belta2005-2012U441F
Caldina 215G1997-2002A241F,A243F+MF1A
Caldina 2402002-2007A248F+MF1A
Camry / Camry Gracia / Mark II Qualis V201997-2001A541F
Camry V302001-2006U140F''
Camry V402006-2011U140F''
Carina 21008.1998-2001A241F,A243F+MF1A
Corolla / Fielder / Runx / Allex 1202000-2006U340F,U341F+MF1A
Corolla Axio / Fielder 1402006-2012K310F, K311F
Corolla Spacio 1202001-2007U341F
Corona 21012.1997-2001A241F,A243F+MF1A
Duet1998-2004-
Matrix 1302002-2006U341F
Opa2000-2005U341F+MF1A
Passo 102004-2010-
Passo 202010-..-
Pixis Epoch/Space2011-..-
Premio / Allion 2402001-2007U341F+MF1A
Premio / Allion 2602007-..K311F
Ractis 1002005-2010U340F
Sienta 802003-2015U340F
Vista 501998-2003U240F+MF1A
Vitz 902005-2010U441F
Voltz2002-2004U341F
Will VS2001-2004U341F


1.4. ATC/DTC type
Basic front-wheel drive, no center differential, the rear wheels are connected via electromechanical coupling


ATC (Active Torque Control) is used by Toyota since 1998, similar to the V-Flex, but the rear wheels connection performs by electromechanical coupling instead viscous. The control system automatically maintains the target value of torque transmitted to the rear wheels ("ATC coupling"). After 2012 at some models the system received the designation "DTC" (Dynamic Torque Control).

Since active implementation of vehicle stability systems (for Japanese brands - from the second half of the 2000s) and the appearance of differential locking emulation via brake system, the new phase of all-wheel drive started. At some manufacturer's models communication of torque-on-demand 4WD and ESP can provide a greater effect than even classic full-time with only center locking, unable to overcome "diagonal". However, comparing the operation of different modern suv at light off-road, we have to admit - effectiveness of Toyota's ATC 4WD and locking emulation are among the worst.

Scheme imperfections:
- quick overheating and disconnection of coupling under load
- low efficiency
- bearings wear ("ATC coupling repair").

system have few variants of control:

• With "AUTO" button (passenger cars and minivans) - operation modes "AUTO 4WD" and "2WD". At OFF state there is only front-wheel- drive, at ON state - control unit automatically manage torque distribution to the rear wheels.


• With "LOCK" button (light suvs) - operation modes "AUTO 4WD" и "LOCK". In AUTO mode control unit automatically manage torque distribution to the rear wheels, at LOCK mode - maintains the highest possible rate of electromechanical coupling locking.

• Without control buttons (some Japan domestic models) - constant automatic control of torque distribution.




ModelProductionTransmission
Alphard / Vellfire 202008-2015U660F
Alphard / Vellfire 302015-..K115F
Auris 1502007-2012K310F,K311F
Auris 1802012-..K310F
Blade 1502007-2012K112F
Corolla Axio / Fielder 1602012-..K310F
Corolla Rumion 150 2007-..K311F
Estima 401999-2006U140F'''
Estima 502006-..U660F'''
Gaia1998-2004A243F+MF1A
Harrier 602013-..K114F
Highlander 502013-..U660F
Ipsum 1004.1998-2001A243F+MF1A
Ipsum 202001-2009A243F+MF1A
Isis2004-..K111F
Ist 1102007-..K310F
Lexus NX2014-..U661F
Lexus RX GGL152008-2015U660F
Lexus RX L202015-..-
Mark X Zio2007-2013K112F
Matrix 1402008-2013U140F''
Nadia1998-2003A243F+MF1A
Noah / Voxy 602001-2007K111F,A248F
Noah / Voxy 702007-2014K111F
Noah / Voxy / Esquire 802014-..K114F
Porte / Spade 1402012-..K310F
Ractis 1202010-..K310F
RAV4 / Vanguard 302006-..K111F,K112F,U151F,U660F
RAV4 402013-..K111F,U660F,U760F
Sienna 302010-..U660F
Sienta 1702015-..K310F
Venza 102008-..U660F, U760F
Vitz 1302010-..K310F
Wish 102003-2009U341F
Wish 202009-..K311F


1.5. VSC+ type
Full-time four-wheel drive, symmetrical center differential, differential locking emulation via brakes


VSC+ is a variation of the STD II scheme without any couplings. Instead, the locking emulation is performed using the ABS/TRC/VSC - slipping wheel is braked, thus torque at the other wheel of same axle is increased. Similarly, the torque is redistributed between the front and rear wheels. The effectiveness of this scheme is really pour even at not severe conditions.

ModelProductionTransmission
Harrier MCU352003-2006U140F'
Highlander 202003-2007U140F'
Highlander 402007-2014U151F
Sienna 202003-2010U151F
Lexus RX MCU352003-2006U140F'+MF2A


: TM - transmission (gearbox, CVT), TR - transfer, FD - front differential, RD - rear differential, CD - center differential, CDC - hydraulic clutch, VC - viscous coupling, EC - electromechanic coupling.


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