Toyota 4WD review (1)

Read in Russian

Eugenio,77
mail@toyota-club.net
© Toyota-Club.Net
Feb 2004 - Feb 2018


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

1.1. Full-time all wheel drive

1.1.1. STD I type

Full-time all wheel drive. Center differential - symmetrical, bevel gears (front/rear torque distribution 50/50), locking - by multi-plate wet clutch with variable lock rate.

A241H gearbox is based on gearbox with simple hydraulic control, its locking principles are less progressive (for details, "A241H automatic transmission"), whereas A540H has real electronic control with feedback (for details, "A540H automatic transmission").

The maximum locking rate is realized at selector lever position "L" and "R".




"C.DIFF AUTO" mode permits control unit to select the locking rate depending on the driving conditions, when auto mode is OFF the center differential remains free. The button is installed at all models with A241H and early models with A540H (since 1994 the button is absent and automatic mode activated permanently).

Standard for everyday driving is the automatic mode, so disabling it is provided only for towing or using the undersized spare wheel.

ModelProductionTransmissionDifferential locking
Caldina 1901992-20024AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina 1901992-19964AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina 2101996-08.19984AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Carina ED 2001993-19984AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corolla / Sprinter 901987-19924AT A241Hcenter - hydromechanical clutch
Corolla / Sprinter 1001992-20024AT A241Hcenter - hydromechanical clutch
Corolla / Sprinter 1101995-20004AT A241Hcenter - hydromechanical clutch
Corolla Spacio 1101997-20024AT A241Hcenter - hydromechanical clutch
Corona 1901992-19964AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corona 2101996-12.19974AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Corona Exiv 2001993-19984AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Ipsum 101996-04.19984AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
RAV4 101994-20004AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch, rear - Torsen (opt.)
Sprinter Carib 951988-19954AT A241Hcenter - hydromechanical clutch
Sprinter Carib 1101995-20024AT A241Hcenter - hydromechanical clutch
Vista / Camry 201988-19904AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Vista / Camry 301990-19944AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch
Vista / Camry 401994-19984AT A540H+AF2BEcenter - electronically controlled hydromechanical clutch

1.1.2. STD II type

Full-time all wheel drive. Center differential - symmetrical, bevel gears (front/rear torque distribution 50/50), locking - by viscous coupling.

Torsen type rear LSD was available as option.


ModelProductionTransmissionDifferential locking
Alphard 102002-20084AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Caldina 215W GTT1997-20024AT U140F+MF2AVcenter - viscous coupling
Caldina 246 GT42002-20074AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Harrier 101997-20034AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Harrier ACU35/GSU3#2003-20134AT U140F+MF2AV
5AT U151F+MF2AV
center - viscous coupling, rear - Torsen (opt.)
Highlander 202000-20034AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Kluger2000-20074AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Lexus RX MCU3#1998-20034AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)
Lexus RX350 GSU3#2006-20085AT U151F+MF2AVcenter - viscous coupling
RAV4 202000-20064AT U140F+MF2AVcenter - viscous coupling, rear - Torsen (opt.)

1.1.3. VSC+ type


Full-time all wheel drive. Center differential - symmetrical, bevel gears (front/rear torque distribution 50/50), free.

The locking emulation is performed using 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.

ModelProductionTransmission
Harrier MCU352003-20064AT U140F'
Highlander 202003-20074AT U140F'
Highlander 402007-20145AT U151F
Sienna 202003-20105AT U151F
Lexus RX MCU352003-20064AT U140F'+MF2A



1.2. Selectable all wheel drive

1.2.1. V-Flex I type


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

The coupling filled with silicone fluid, connects the two parts of the intermediate propeller shaft and operates when a significant slip of the front wheels occurs, at other times the car remains front-wheel drive.

ModelProductionTransmission
bB 302000-20054AT U340F
Funcargo1999-20054AT U340F
Ist 602002-20074AT U340F
Platz1999-20054AT U340F
Porte 102004-20124AT U340F
Probox / Succeed 502002-20144AT U340F
Probox / Succeed 1602014-..CVT K310F
Raum 101997-20034AT A244F+CF1A
Raum 202003-20114AT U340F
Starlet 801989-19964AT A244F+CF1A
Starlet 901996-19994AT A244F+CF1A
Tercel / Corsa / Corolla II 401990-19944AT A244F+CF1A
Tercel / Corsa / Corolla II 501994-19994AT A244F+CF1A
Vitz 101999-20054AT U340F+MF1A
Will Cypha2002-20054AT U340F

1.2.2. V-Flex II type


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

The coupling filled with silicone fluid, connects the propeller shaft to the input shaft of the rear differential and operates when a significant slip of the front wheels occurs, at other times the car remains front-wheel drive.


ModelProductionTransmission
Avensis 2502003-20084AT A248F
bB 20*2006-2016-
Belta2005-20124AT U441F
Caldina 215G1997-20024AT A241F,A243F+MF1A
Caldina 2402002-20074AT A248F+MF1A
Camry / Camry Gracia / Mark II Qualis V201997-20014AT A541F
Camry V302001-20064AT U140F''
Camry V402006-20114AT U140F''
Carina 21008.1998-20014AT A241F,A243F+MF1A
Corolla / Fielder / Runx / Allex 1202000-20064AT U340F,U341F+MF1A
Corolla Axio / Fielder 1402006-2012CVT K310F, K311F
Corolla Spacio 1202001-20074AT U341F
Corona 21012.1997-20014AT A241F,A243F+MF1A
Duet*1998-2004-
Matrix 1302002-20064AT U341F
Opa2000-20054AT U341F+MF1A
Passo 10*2004-2010-
Passo 20*2010-2016-
Passo 700*2016-..-
Pixis Epoch*2012-2017-
Pixis Joy*2016-..-
Pixis Mega*2015-..-
Pixis Space*2011-..-
Premio / Allion 2402001-20074AT U341F+MF1A
Premio / Allion 2602007-2014CVT K311F
Ractis 1002005-20104AT U340F
Sienta 802003-20154AT U340F
Tank / Roomy*2016-..-
Vista 501998-20034AT U240F+MF1A
Vitz 902005-20104AT U441F
Voltz2002-20044AT U341F
Will VS2001-20044AT U341F
* - Daihatsu models, sold under Toyota brand

1.2.3. ATC / DTC type


Basic front-wheel drive, no center differential, the rear wheels are connected via multi-plate electromechanical coupling.

The coupling connects the propeller shaft to the input shaft of the rear differential. In most cases, the car remains front-wheel drive, but if necessary, the control system automatically maintains the target value of torque transmitted to the rear wheels (for details, "ATC coupling").
The original name is "Active Torque Control", since 2012 at some models the system receives the designation "Dynamic Torque Control".

There are several options of driver's 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" "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) - all-time automatic control of torque distribution.

ModelProductionTransmission
Alphard / Vellfire 202008-20156AT U660F
Alphard / Vellfire 302015-..CVT K115F
Auris 1502007-2012CVT K310F,K311F
Auris 1802012-..CVT K310F
Blade 1502007-2012CVT K112F
C-HR2016-..CVT K313F
Corolla Axio / Fielder 1602012-..CVT K310F
Corolla Rumion 150 2007-2016CVT K311F
Estima 401999-20064AT U140F'''
Estima 502006-..6AT U660F'''
Gaia1998-20044AT A243F+MF1A
Harrier 602013-..CVT K114F
Highlander 502013-..6AT U660F
Ipsum 1004.1998-20014AT A243F+MF1A
Ipsum 202001-20094AT A243F+MF1A
Isis2004-..CVT K111F, K311F
Ist 1102007-2016CVT K310F
Lexus NX2014-..6AT U661F
Lexus RX GGL152008-20156AT U660F
Lexus RX AL202015-..6AT U661F, 8AT U881F
Mark X Zio2007-2013CVT K112F
Matrix 1402008-20134AT U140F''
Nadia1998-20034AT A243F+MF1A
Noah / Voxy 602001-2007CVT K111F, 4AT A248F
Noah / Voxy 702007-2014CVT K111F
Noah / Voxy / Esquire 802014-..CVT K114F
Porte / Spade 1402012-..CVT K310F
Premio / Allion 2602014-..CVT K311F
Ractis 1202010-2016CVT K310F
RAV4 30 / Vanguard2006-2016CVT K111F,K112F, 5/6AT U151F, U660F
RAV4 402013-..CVT K111F, 6AT U660F,U760F
Sienna 302010-..6AT U660F
Sienta 1702015-..CVT K310F
Venza 102008-..6AT U660F, U760F
Vitz 1302010-..CVT K310F
Wish 102003-20094AT U341F
Wish 202009-..CVT K311F

1.2.4. DTV type


Basic front-wheel drive, no center and rear differentials, the rear wheels are connected via independent clutches.

In most cases, the car remains front-wheel drive, if necessary the control system automatically adjusts the value of the torque transmitted to each of the rear wheels. In addition, the mechanism designed for disconnection of powertrain in the transfer case and in the rear axle, so that the propeller shaft and gears are not rotated in 2WD mode.

The official name - "Dynamic Torque Vectoring AWD", the drive type is presented in 2018.



1.3. Electrical all wheel drive

1.3.1. E-4WD type


Basic front-wheel drive, without a mechanical link between the axles, the rear wheels are driven by a separate electric motor.

Two types of rear power modules are used - the classic three-shaft (several power and torque variants) and a compact two-shaft with a low-power electric motor (HV4WD).


ModelProductionRear motor (kW/Nm)
Alphard ATH102003-20081FM (18/108)
Alphard/Vellfire ATH202008-20152FM (50/130)
Alphard/Vellfire AYH302015-..2FM (50/139)
Estima AHR102001-20061FM (18/108)
Estima AHR202006-..2FM (50/130)
Harrier MHU382005-20122FM (50/130)
Harrier AVU652013-..2FM (50/139)
Highlander MHU282005-20072FM (50/130)
Highlander MHU482007-20102FM (50/130)
Highlander GVU482010-20142FM (50/130)
Highlander GVU582014-..2FM (50/139)
Kluger MHU282005-20072FM (50/130)
Lexus RX400h MHU382005-20082FM (50/130)
Lexus RX450h GYL152009-20152FM (50/130)
Lexus RX450h GYL252015-..2FM (50/139)
Lexus NX300h AYZ152014-..2FM (50/139)
Prius ZVW552015-..1MM (5.3/55)
RAV4 AVA442015-..2FM (50/139)

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



Development, efficiency, reliability

The history of Toyota 4WD for the initially FWD cars started in 1988.

STD I type, which appeared in the most boom years of the Japanese automotive industry, remains the most perfect, reliable and efficient among all variations of the all-wheel drive of Toyota road cars. This "Full-Time 4WD" really was a permanent, "full" and, importantly, built on the basis of problem-free and steady automatic gearboxes. The only fundamental drawback (by modern standards) is the absence of any axle differential lockings, which makes the cars sensitive to conditional diagonal. Alas, the production of the last STD I models was finished in 2002.

For the B-class models Toyota used part-time 4WD (V-Flex I) from the late 1980s until the 2010s. Currently, this type is applied to the only utilitarian model of Toyota.

The protracted crisis of the 1990s made a total economy as a new trend - economy on materials, useful options, and, of course, construction perfections. The break of Toyota 4WD came after 1997 - with the start and massive implementation of V-Flex II, one of the most advanced systems changed to the most primitive. Its drawbacks are well known:
- delayed "operation" of viscous coupling,
- limited locking ability,
- potential danger when active driving,
- limited coupling lifetime.
Of course, even such a dubious 4WD remained preferable to a mono-drive, but the problem is that experienced owners had something to compare with. Since 2015, the V-Flex II is no longer used for the models developed by Toyota itself, and remains an attribute of only Daihatsu rebaged models.

The most common type of all-wheel drive in the world - with the electromechanical coupling - was introduced for Toyota in 1998 (ATC). Initially - for minivans, but gradually it came to the lower classes, replacing V-Flex, and to the SUV class, eliminating the remnants of full-time.. Drawbacks of this type:
- limited locking ability,
- limited operation time under load,
- wear of the coupling bearings ( for details, "ATC coupling repair").
In general, the effectiveness of ATC does not reach a full-time AWD, but significantly exceeds V-Flex.

It is worth noting one more thing - the end of the 1990s was marked by the appearance of new Toyota / Aisin transmissions (the latest versions of A24# serie, U-series), the service life of which, compared to its predecessors, drastically decreased, which was especially noticeable for more loaded AWD vehicles. As a result, 4WD transmissions became not only less efficient, but at the same time less reliable.

For the class of SUVs / crossovers just started at that time, Toyota retained the full-time in the simplest version (STD II), which actually borrowed from the previous models with mechanical gearboxes (except that installing five satellites instead of four in the center differential). The expected low efficiency of viscous couplings in comparison with hydromechanical ones affected the performance in this case too.

By the middle of the 2000s, the development of technology allowed to completely abandon viscous coupling, leaving all three differentials free (VSC+) - now the lockings were emulated using the brake system. This type remained in production not too long and soon all the crossovers received ATC 4WD.

In general, the implementation of vehicles stability systems (Japanese brands - since the second half of 2000s) and the appearance of difflock emulation by brakes, a new stage of 4WD development began in the world. Some manufacturer's selectable 4WD and ESP gives a better effect than even some versions of the full-time with an excessively "soft" center locking or its emulation. But not in the case of Toyota - comparing the actual behavior of modern SUVs of different brands it is necessary to recognize - Toyota's settings of the selectable 4WD and difflock emulations are extremely unsuccessful.

Not in the best way the rejection of AT in favor of CVT reflected on the performance of the all-wheel drive, which continues since the mid 2000s (mono-drive versions received CVT even earlier). This is not so important for light cars, but for minivans and, especially, crossovers, CVT becomes the narrowest, most vulnerable and expensive part of the power transmission circuit between the engine and wheels.

Another type of conditionally all-wheel drive known since 2001, has formed by numerous hybrid models (E-4WD). With the external temptation of the idea, the nice values and the diagrams of the rear motor torque, in reality the traction capabilities did not meet expectations - E-4WD efficiency does not even reach ATC of similar non-hybrid models.

Own "torque vectoring" type (DTV) Toyota introduced only in 2018, eight years later than Nissan, almost fifteen later than Honda and two decades after the MMC. Potius sero quam nunquam.










x