All Wheel Driven - Everything About All Wheel Drive

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Alfa-Romeo

155 - ?

Figure: Alfa-Romeo 155 q4

164 q4 - ?

Figure: Alfa-Romeo 164 q4 rear differential with "Viscomatic" unit.

Figure: Gearbox with power takeoff to the rear wheels

Figure: All wheel drive control diagram

Last updated: 2010-01-20 23:30

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Audi

Audi 80/90 quattro, Audi Quattro, Audi UrQuattro 1981-1987 - First quattro generation. Full-time all wheel drive with free differentials. Manually locking (by 2 rotating switches on the console) rear and center differentials.

Figure: Audi 80 B3 quattro

Figure: Audi Quattro

Figure: quattro I transmission. On the top picture: center differential (5), center differential locking fork shaft (6), differential locking actuator (7)

Audi 80/90/100 quattro 1987-1994 - quattro II. Full-time all wheel drive. Torsen center differential with automatic distribution of torque between front and rear axles. Manually activated (electro-pneumatic system) rear locking differential which automatically unlocks when speed exceeds 25 km/h.

Figure: Audi 80 B4 quattro

Figure: quattro II transmission with TorSen center differential

Audi V8 Manual 1988-1994 - quattro III - Full-time all wheel drive. Torsen center differential, Torsen rear differential, free front differential.

Audi V8 Automatic 1988-1994 - quattro III - Full-time all wheel drive. Torque distribution via electronically controlled multi-plate hydraulic transfer clutch in the center. Torsen differential in the rear axle. Quattro was for the first time used with automatic transmission. The gearbox was the source for high pressure oil, that was used to activate the clutch.

Audi A4/A6/A8/Allroad quattro 1994-2007 , S4/S6 quattro 1994-2005 - quattro IV - Full-time all wheel drive. Torsen center differential. Electronic traction control (EDL) on front and rear axles that applies brakes to spinning wheels, which has effect of locking front and rear differentials. Works at speeds up to 40 kph (25mph). On more powerful versions S4/S6 - up to 80 kph (50mph). A8 uses EDL and ASR, which reduces engine output. It is almost impossible to lose traction with this system under any circumstances.
Audi Allroad can feature low gearing (optional).

Figure: Audi A4 B6 quattro

Audi RS4 B7 manual/Q7 2005-..., S4 B7 manual 2006-..., A5 2006-..., A6 2006-...(verify), all A4 B8 2007-... - quattro V. Full-time all wheel drive. Torsen type III planetary type differential with a 40front/60rear split for improved handling.

Audi A3/S3 quattro (1998-2003) - Haldex Generation I automatic all wheel drive system - electronically controlled Haldex multi-plate hydraulic clutch, located near the rear differential. Normally front wheel drive vehicle. It detects the need of all wheel drive at 1/8 of the wheel spin and transfers up to 100% of torque to the rear axle.

Audi A3/S3 quattro (2003-2008) - Haldex Generation II automatic all wheel drive.

Audi A3/S3 quattro (2008-...) - Haldex Generation IV automatic all wheel drive.

Audi TT quattro (1998-2006) - Haldex Generation I automatic all wheel drive. Haldex Generation II automatic all wheel drive since 2002.

Audi TT quattro (2006-...) - Haldex Generation IV automatic all wheel drive.

BMW

3-series E30 325iX 1988-1992 - Full-time all wheel drive. Viscous coupling locking center differential with torque split 37% front / 63% rear. The viscous coupling is integrated into the planetary gear center differential. Viscous coupling locks the differential when wheel slipping occurs and transfers up to 90% of torque to the axle that has traction. Viscous coupling locking rear differential distributes torque between the rear wheels.

Figure: BMW E30 325iX transfer case

Figure: BMW 325iX

Bucher

DURO -

The DURO is a highly mobile all-terrain military tactical vehicle. The name DURO stands for DUrable and RObust.

Figure:

Last updated: 2010-01-10 17:02

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Bugatti

Veyron 2004-... - Haldex automatic all wheel drive.

Last updated: 2010-01-09 18:39

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Cadillac

Escalade 1999 - Automatic all wheel drive with 2wd, and 4wd lock modes and low gear. Based on Tahoe/Yukon/Denali platform. NVG 246 "AutoTrac" four wheel drive system. 2Hi, Auto 4wd (100% of torque is transferred to rear wheels until it detects a need for extra traction. Dry multi-plate clutch is used to transfer torque to the front), 4Hi (50/50 split - dry multi-plate clutch is locked), 4Lo (2.72:1 low range gear). All 4wd modes are button activated.

Last updated: 2010-01-09 18:39

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Chevrolet

Tracker (Suzuki Vitara) 1999-2005 - Part-time all wheel drive. Lever-operated two-speed part-time transfer case. 1.82:1 low gear. From 1999- new vacuum-actuated front axle disconnect, which eliminates the need of backing-up to disengage the the front hubs.
Corporate IFS open differential axle up front, corporate rear live axle equipped with limited slip (open differential rear on Tracker).

Tahoe - Automatic all wheel drive with 2wd, and 4wd lock modes and low gear. NVG 246 "AutoTrac" four wheel drive system. 2Hi, Auto 4wd (100% of torque is transferred to rear wheels until it detects a need for extra traction. Dry multi-plate clutch is used to transfer torque to the front), 4Hi (50/50 split), 4Lo, all button activated. 2.72:1 low range gear.(3,73 optional).
GM's 10 bolt IFS front with Central Axle Disconnect (CAD)
GM's corporate 10-bolt live axle with g80 limited slip (opt) and 3.73:1 gears.

Silverado - 2 versions can be used: manually actuated part-time 4wd or "AutoTrac" (See Chevy Tahoe)

Last updated: 2010-01-09 18:39

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Citroen

Visa -

Last updated: 2010-01-10 17:26

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Fiat

Fiat Ducato -

Fiat Tempra -

Last updated: 2010-01-10 18:22

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Ford europe

Ford Mondeo 4x4 - full time all wheel drive with 58/42% torque split (front to rear ?)

Figure: Ford Mondeo (??) center differential

Figure: Ford Mondeo (??) planetary gear center differential (what year??)

Ford Scorpio 4x4 - Full-time all wheel drive.

The constant drive was realized as follows. Behind the common 5-speed gearbox, the ZF transfer gearbox with interaxle differential was mounted. Planetary gear set of the interaxle differential distributed the torque in 37/63-front/rear ratio. The differential included viscous coupling with lock-function. To the rear, the transfer gearbox extended in two-section cardan shaft propelling the rear axle with bevel gear differential and axle shafts with CV joints. The rear axle differential included viscous coupling with lock-function for improved traction. Front axle propulsion comes out of the transfer gearbox aside the engine axe. There is a 1:1 chain transmission.

The transfer gearbox is connected to front bevel gear differential using short cardan shaft. The front differential is mounted on crankcase, therefore the propulsion of front left wheel must have been constructed using a shaft leading through crank case. The shaft was split into two parts to ensure smooth and reliable operation. The parts used in this configuration are rather special and therefore expensive.

On all 4WD cars, the most powerful motors were mounted only, at first 2.8 (till 1987, very rare car), then 2.9litr (engine equipped with catalys. has torque - 229 Nm, than 222 Nm, at standart engine). Also You can understand that you have business with 4x4 before 1990, thanks to black windows ornament. Also 4x4 version was produced as GL and as Ghia set. After 1990 only in GL version (not in England). All 4x4 cars was equipped with 5-speed manual gearbox. Main bodyes was: hatch and saloon, but there was also Tournier version, but it's a very rare car, I have met only 1 in my life.
Oh, yes, 4x4 technic was designed by Fergusson, it's very famous firm, and it's helped to Ford with Sierra 4x4 also.

A - rear axle
B - epicycle drive
C - viscomate
D - drive chain in the distributive drive
E - gearbox's band wheel shaft
F - driving shaft to the front axle's distributive drive
G - front axle's distributive drive
H - front axle

Source: www.fordscorpio.ee

Sierra XR 4x4 - Full-time all wheel drive, 40% front / 60% rear (35/65% ??) torque distribution under normal conditions.

Figure: Sierra 4x4 layout

Figure: Sierra 4x4 front differential

Figure: Fergusson type center viscous coupling (5) locking differential (4)

Ford RS200 1984-1986 -

Transit (2006-...) - Automatic all wheel drive. Normally rear wheel drive vehicle. When rear wheels slip, torque is transferred to the front wheels via two multi plate clutches, installed in the front axle - one clutch for each of the front wheels. Each clutch incorporates an Eaton-type oil pump.

http://www.gizmag.com/go/6198/

Last updated: 2010-03-07 19:30

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Ford USA

Expedition

Figure: Ford Expedition (2003) vacuum-disconnected front hubs.

Last updated: 2010-01-16 23:54

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Honda

CR-V, HR-V 1996-... - Automatic all wheel drive. Honda's Real Time Four Wheel Drive System. Normally front wheel drive vehicle. Torque transfer to rear axle via multi-plate clutch. Dual pump system is used to apply pressure to the clutch. It also disengages the clutch when braking to allow ABS work smoothly.

Figure: Honda's rear differential with dual pump system and multi-plate clutch.

Figure: Honda's dual pump system

Figure: Honda CR-V

Figure: Honda HR-V

How Honda's Dual Pump 4WD works

For most of the time, only the HR-V’s front wheels are driven; it’s only when they begin to lose grip that the Dual Pump system starts to send power to the rear wheels. This is achieved by a hydraulic torque-split system, consisting of a conventional front-wheel drive arrangement, complete with transfer case, a propeller shaft running the length of the vehicle and a Dual Pump system integrated with the rear differential. This is the heart of the system and comprises two hydraulic pumps, one driven by the front wheels via the prop shaft, the other by the rear wheels via the rear differential.
During normal levels of grip the front and rear wheels, and their respective pumps, turn at the same speed; hydraulic pressure circulates between the two pumps, but no pressure is generated. If the front wheels begin to lose traction and start to spin faster than those at the rear, the two pumps turn at different rates; hydraulic pressure proportional to the difference in their speeds is generated, which in turn opens a valve body and activates a mechanical, multi-plate clutch.
This clutch then connects the front prop shaft to the rear diff, which feeds precisely the correct amount of torque to the rear wheels to re-establish overall traction. The more the front wheels slip, the greater the torque fed to the rear wheels.
The Dual Pump arrangement weighs less than a conventional four-wheel drive system and demands little maintenance – just a fluid change at 72,000 miles and thereafter every 36,000 miles. Further advantage of this design is that it automatically disengages under braking, thereby allowing the ABS to operate.

Source: www.theaa.com

Honda's SH-AWD all wheel drive system (Honda Legend 2004-...) - Super Handling All-Wheel-Drive system (SH-AWD).

By monitoring driver input and driving conditions, the SH-AWD system determines the optimum front-rear and lateral (left-right) torque distribution. This information is then conveyed to the rear differential, where direct electromagnetic clutches continuously regulate and vary front-rear torque distribution between ratios of 30:70 and 70:30, and lateral torque distribution in the rear wheels between ratios of 100:0 and 0:100. Torque is used not only for propulsion, but for cornering as well, resulting in a significant enhancement in vehicle maneuverability.

How front-to-rear torque is distributed:

Straight-line driving front-rear torque distribution is regulated for optimum performance in accordance with the amount of torque produced. During rapid acceleration the load on the front wheels is reduced; conversely, rear-wheel load is reduced during cruising. The result is stable driving at all times.

How left-to-right torque is distributed on the rear wheels:

During cornering, torque to the rear wheels is continuously varied to supply up to 100% to the outside wheel and 0% to the inside wheel. This creates an inward yaw moment, significantly improving vehicle handling. Yaw moment is turning torque relative to the vertical axis running through the vehicle’s center of gravity.

When decelerating during cornering (throttle closed), torque to the outside rear wheel is freely varied to change from an inward to an outward yaw moment, ensuring vehicle stability at all times.

How does acceleration device works:

The rear differential is also equipped with a built-in acceleration device. During cornering, the track of the outside rear wheel normally falls outside the average of the tracks of the front wheels. The outside rear wheel does not rotate fast enough to keep up with the front wheels, preventing efficient transmission of torque. To counteract this problem, the SH-AWD acceleration device alters the gearing to speed up the outside rear wheel’s rotation relative to the front wheels. This reduces torque transmission losses and significantly improves vehicle maneuverability. During straight-ahead driving, the twin-pinion planetary carrier spins in synchronization with the propeller shaft, causing the front and rear wheels to turn at the same speed. When the vehicle enters a curve, however, the planetary carrier is locked to the case, releasing the device from synchronization with the propeller shaft and accelerating the rotation speed of the rear wheels. A hydraulic actuator which turns the clutches on and off, and a one-way clutch are included in this compact configuration.

Source: http://world.honda.com/news/2004/4040401.html

Watch Honda's video about SH-AWD: http://world.honda.com/HDTV/news/2004-4040401a/

Last updated: 2010-03-07 20:16

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Hummer

Hummer I - Full-time all wheel drive.

Transfer case:
All HUMMERs use a New Process Gear (NPG) 242 2sp transfer case. It is a full time transfer case incorporating an open differential between the front and rear driveshafts (DS). It has 4 modes, High (H), High Locked (HL), Low (locked) (L), and Neutral (N). The ratios are 1:1 in high, 2.72:1 low.
The input shaft and rear output shaft are co-linear. The front is a left handed output, chain driven.
In H, the normal operating position, torque is evenly split front and rear via the transfer case's differential. This center differential is open and allows the front and rear driveshafts to turn at different rates to allow turning on high traction surfaces. In HL, the differential is locked (manual locker), forcing the front are rear driveshafts to turn at the same rate. This is equivalent to a part-time 4wd system. The L position forces the input shaft to turn a planetary gear assembly at the front of the case. The ring gear is machined into the front case. Low adds a gear reduction of 2.72:1. The differential is always locked in low. The N position disconnects the input from the output shafts totally. The differential is open in this position.
A sensor at the rear of the transfer case (TC) is used to determine speed. Another sensor determines if the TC differential is locked or unlocked, illuminating a status light.
The TC is cooled via transmission fluid flowing through an intercooler inside the TC.
The engine, transmission, and transfer case are rigidly connected together. The assembly is canted slightly to the right.
Differentials
The differential case is a Dana (AMC) 20, hypoid (top entry), same as in some older Jeeps (AFAIR). The differential has a ratio of 2.73:1. HUMMERs use Zexel-Gleason Torsen torque sensing/biasing differentials. These are not a limited slip design or locking design. The bias ratio is 3.8:1 AFAIK. Since the suspension is independent, the differential case is connected to the frame.

Source: Gerald's HUMMER Page

Hummer II

Hummer III

Last updated: 2010-01-09 18:39

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Hyundai

Santa Fe I 2.7V6, 2.0 diesel 2001-2006 - Full-time all wheel drive. Developed by Steyr-Daimler-Puch. A viscouse coupling locking planetary differential inside the front transaxle splits the drive torque equally between the front wheels, and 60/40 between the front and rear axles.

Figure: Hyundai Santa Fe I Steyr-Daimler-Puch full-time all wheel drive system

Santa Fe I 3.5V6 2002-... - Automatic all wheel drive. The BorgWarner TorqTransfer System ITM-I (interactive torque management I). The system uses electronic sensors and microcomputer controls to sense slippage in a vehicle's front wheels and automatically transfers power to the rear wheels. Then, when the front wheels are no longer slipping, the system reduces or eliminates power to the rear wheels.

The reduced slippage increases efficiencies that enhance vehicle handling and traction and improve fuel economy. The ITM-I can work with other systems such as antilock brake systems and electronic stability programs to further enhance traction and stability.

SantaFe II 2006-..., Tuscon 2004-2009 - Automatic all wheel drive. The Borg Warner ITM 3e, an electromagnetic clutch-type system that sends 95% of the power to the front wheels—until they encounter a low traction situation, when up to 50% of the power can be apportioned rearward.

Figure: Hyundai SantaFe II/Tuscon electromagnetic clutch attached to the rear differential case.

Last updated: 2010-01-23 14:05

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Isuzu

Amigo (Opel Frontera) - Part-time all wheel drive. Lever-operated part-time two-speed transfer case with Neutral position. 4x4 button to engage the front axle (CAD). 2.05:1 low range gear. Front - corporate IFS with open differential. Dana 44 solid rear axle with limited slip.

Trooper 1993 - Part-time all wheel drive. Manual front free hubs, automatic hubs - optional. Rear manually lockable differential - optional. 2,28:1 low gear ratio.

Trooper 1999-..., Vehicross 1999-... - Automatic all wheel drive. TorqueOnDemand system, developed by Borg-Warner.D distribution of power to the front wheels is infinitely variable from 0 to 50%. Computer-controlled multi-plate clutch works as quickly, as in 20 ms. 2,48:1 low gear. Limited slip differential rear.

SUZU's TORQUE-ON-DEMAND ® (TOD) is unlike any drive system ever offered on an Isuzu vehicle. This patented system is an automatic 4WD system that provides the best aspects of part-time and full-time 4WD systems without their compromises. TORQUE-ON-DEMAND is standard equipment on the VehiCROSS and all 1999 Troopers with automatic transmissions (All S, Performance and Luxury Packages).

How TOD Functions When You're Driving

When TOD is activated and the transfer case is in the High range position and TOD is turned on, the TOD control unit receives signals sent from the 12 input sensors, including front and rear axle speed sensors, ABS brake switch and the throttle position sensor. Isuzu's proprietary 3-D mapping software uses that input to determine the amount of force that's applied to the clutch pack.
When the clutch is completely disengaged, only the rear wheels are driven; when the clutch is completely engaged, a 50/50 torque split is achieved (50% of the power goes to the front wheels and 50% to the rear wheels). The amount of torque transferred to each axle (torque split) varies continuously as conditions are changing. Torque demands are continuously (every 20 milliseconds) monitored and redistributed as needed, providing unmatched efficiency.
If the rear wheels begin to slip, the control unit detects the slippage and determines the optimum level of torque based on the feedback control logic, and then increases the torque to the front wheels.

What Makes It Different

This system even has the ability to "anticipate" certain driving situations. Using the signal from the throttle position sensor, including acceleration and deceleration, it determines the torque distribution that will be needed. That means an Isuzu vehicle equipped with TORQUE-ON-DEMAND can virtually anticipate road conditions, so it's ready before you realize you need it. For example, if a driver is going down a hill and takes his foot off the accelerator, the TOD system automatically increases torque to the front wheels to improve handling and evenly distribute engine braking to all four wheels. All this happens automatically -- without the driver sensing any changes.

Unlike other all-wheel drive systems, there's a special display on the instrument panel that provides the driver with active feedback. This display shows the performance of the system and the varying degrees of torque split to keep the driver informed of varying conditions that might otherwise go unnoticed.

There are three lights on the TORQUE-ON-DEMAND display; they represent:

No bars illuminated: approximately 100% rear-wheel drive;
0% front-wheel drive.

One bar illuminated: approximately 85% rear-wheel drive;
15% front-wheel drive.

Two bars illuminated: approximately 70% rear-wheel drive;
30% front-wheel drive.

Three bars illuminated: approximately 50% rear-wheel drive;
50% front-wheel drive.

Source: http://www.autoworld.com/news/Isuzu/Torque.htm

Last updated: 2010-01-16 23:57

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Jaguar

X-Type - Full-time all wheel drive.

Last updated: 2010-01-16 23:58

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Jeep

Grand Cherokee SRT8 2006-2009 - pro-active automatic all wheel drive. In normal conditions, 100% of torque is transferred to the rear axle. This system is sold under the name of Quadra-Trac I, however it is not a full-time all wheel drive, as on the other Grand Cherokees.

Grand Cherokee WK 2005-..., Commander XK 2006-... - Equipped with one of the following four wheel drive systems:

Quadra-Drive II - full-time all wheel drive system. 48/52 percent torque split (front/rear). Electronically-controlled multi plate clutch pro-actively locks the center differential. 2.72:1 low-range mode. Electronic Limited Slip Differentials (ELSD) front and rear.

ELSD is the Eaton EGerodisc - a hydraulically-operated electronically controlled limited slip differential that is capable of providing variable torque up to full axle lock:
Quadra-Trac II - Same as Quadra-Drive but without the ELSD. Instead, an electronic traction control - Brake Traction Control System (BTCS) - is used to transfer torque from left to right.

See: WK Grand Cherokee 4x4

Grand Cherokee WJ 1999-2004 - Equipped with one of the following four wheel drive systems:

Quadra-Drive - automatic all wheel drive (standard on "Limited", optional on "Laredo"). Normally rear-wheel drive vehicle. The differential is the hydromechanical system based on geroter oil pump and clutch pack, located within the transfer gearbox between the driveshafts that carry power to the front and rear axles. One part of the pump, the rotor, is driven by the front driveshaft while the other part, it's case, is attached to the rear driveshaft. The system reacts faster than the viscous coupling unit of the previous Jeep AWD system. The reaction time is about 40 milliseconds. The transfer box can be also locked in low-range mode to provide equal power to the front and rear axles.
Progressive Vari-Lok gerodisc differentials front and rear, using the same geroter pump system. Almost 100% of torque can be transferred to any wheel.
NV247 AWD transfer case with lever-operated 2.72:1 low-range gear.
Dana 30 non-disconnect live axle at front, aluminum central section Dana 44 at rear.
Quadra-Trac II - automatic all wheel drive. NV247 transfer case. The same as Quadra-Drive but without the Vari-Lok differentials.
Quadra-Trac I - automatic all wheel drive. NV140 - a version of the NV247 transfer case lacking neutral and low-range modes (2004 only).

See: WJ Grand Cherokee 4x4

Grand Cherokee ZJ 1993-1998 - Equipped with one of the following four wheel drive systems:

Command-Trac - part-time all wheel drive with shift-on-the-fly possibility (used until 1996). 2.72 low range.
Selec-Trac - selectable all wheel drive. NV242 transfer case.
Quadra-Trac - full-time all wheel drive system. A viscous coupling locking center differential.
In 1993-1995 the viscous coupling was used to lock the differential when in low range (NP249 transfer case). In 1996-1998 the differential is mechanically locked when in low range (NV249 transfer case).

Figure: Jeep Grand Cherokee Quadra-Drive II (? not sure, needs verification)

See: Four wheel drive systems by vehicle

See: Wikipedia

Last updated: 2010-01-20 23:26

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Kia

Sportage - Part-time all wheel drive. WARN vacuum-operated front wheel hubs, similar to Ford Explorer and Ranger. Rear corporate solid axle with a clutch-type limited slip differential.

Sorento 2002-... - button-operated Part-time all wheel drive. Optional Torque on Demand automatic all wheel drive system. Limited-slip rear differential on LX model (needs verification).

Last updated: 2010-01-09 18:39

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Lada

Niva 1977-... - Full-time all wheel drive with free differentials. Lever-activated low gear. Manually lever-activated locking center differential.

Last updated: 2010-01-09 18:39

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Lamborghini

Diablo VT - Full-time all wheel drive with Viscous Coupling Locking Center Differential

Last updated: 2010-01-09 18:39

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Lancia

Lancia Delta HF - Full-time all wheel drive.

Transmission type

Full-time all wheel drive with centrally-mounted epicyclic torque converter and Ferguson viscous joint; Torsen-type rear differential with 5 to 1 wheel torque ratio

Three differentials are at the heart of the system. Drive to the front wheels is linked through a free-floating differential; drive to the rear wheels is transmitted via a 56/44 front/rear torque-splitting Ferguson viscous-coupling-controlled epicyclic central differential. The real innovation as far as production cars are concerned however, lies between the rear wheels.

The Torsen (torque sensing) rear differential is similar to that found on McLaren Formula 1 cars. The result of combining these differentials in this configuration is an automatic-thinking four-wheel-drive system which requires no manual input from the driver, yet ensures maximum potential traction at any given time.

The Torsen differential is a true 'intelligent' differential in the way it distributes torque. It divides the torque between the two wheels according to the grip available and it does it without ever locking fully; maximum lockup is 70 per cent.

Standard differentials are either free-floating or self-locking. Free-floating systems are good at differentiating between wheel speeds on bends, but always supply the same amount of torque to both wheels. In this situation, however, there is a risk that the wheel with the lighter load (on an incline, for example) or less grip, will lose traction. To counteract this possibility, totally self-locking differentials ensure that both wheels rotate at the same speed but in doing this, prevent free differentiation in cornering, to the detriment of handling and stability.

	Lancia Delta HF 4x4	8 valve HF Integrale	16 valve HF Integrale
Final drive ratio	2.944:1	3.111:1	3.111:1
Torque split front	56%	56%	47%
rear	44%	44%	53%

Figure: Lancia Delta HF 4wd

Figure: Lancia Delta HF Integrale rear TorSen locking differential (lower left), viscous coupling(2) locking planetary gear center differential(1) (lower right). On the top - manually locking rear differential for Integrale?? (what year?)

Lancia Delta / Lancia Dedra / Fiat Tempra / Alfa Romeo 155 -

Figure: Lancia Delta / Lancia Dedra / Fiat Tempra / Alfa Romeo 155 4wd power distribution unit. Planetary center differentical is located on the left, near the left driveshaft. Viscous coupling is located on the right side near the right driveshaft.

Figure: Lancia Delta / Lancia Dedra / Fiat Tempra / Alfa Romeo 155 4wd power distribution unit. 100% of the power goes to the planetary center differential (red), from there, the power is distributed between the front axle (yellow) and the rear axle (blue). When slipping occurs, the viscous coupling locks the front and rear shafts together. The engine is rotating the outer gear of the planetary gear center differential. Power to the front wheels is taken from the sun gear (center gear). Power to the rear wheels is taken from the planet gears (the smallest gears in the middle).

Figure: Lancia Delta / Lancia Dedra / Fiat Tempra / Alfa Romeo 155 4x4 center differential unit.

Lancia Delta S4 - ?

Figure: Lancia Delta S4 four wheel drive

Lancia y10 4wd - Part-time all wheel drive. Button-operated. Vacuum-operated rear axle disconnect system. When in 2wd mode, the driveshafts are disconnected from the transfer box and from both rear wheels.

Last updated: 2010-02-19 23:42

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Land Rover

Defender - Full-time all wheel drive. Lever-operated manually locking center differential.

Figure: Land Rover Defender transfer case

Discovery I - Full-time all wheel drive. Lever-operated manually locking center differential. The chassis are the same as on Defender.

Discovery II - Full-time all wheel drive. Four-wheel electronic traction control. Active cornering enhancement system. Hill Descent Control (HDC). Full-floating live axles front and rear. Unlike on the MB ML-class - it needs only 1/4 - 1/2 of wheelspin to detect the need of traction control activation.

The linkage between the Hi/Lo and diff lock engagement lever was removed on Discovery II, because the traction control system was supposed to perform the functions of locking differentials and Land Rover believed a real differential lock was not needed. However, eearly Discovery still have the transfer box internals. It is possible to order the linkage and connect the differential lock lever (http://www.discovery2.co.uk/diff_lock.html).

Then differential locking mechanism was removed from the transfer case, but introduced again by the end of Disco II life.

Freelander - Automatic all wheel drive. Normally front wheel drive vehicle. Power distribution to the rear via viscous coupling.

Freelander 2006-... - Haldex generation III Automatic all wheel drive.

Series I 1948-1954 - there was a 4wd system without center differential in the beginning, with freewheeling device up front for tire-scrub reduction. From 1950 - dogleg clutch is used to disengage the front axle.

Range Rover 1970-1996 - Full-time all wheel drive. Manually lockable center differential (50/50 power split). Low gear.

Range Rover 1998- - Full-time all wheel drive with viscous control unit in the center and traction control (ETC)

Last updated: 2010-01-31 22:13

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Lexus

RX300 - sold with front wheel drive or full-time all wheel drive. Viscous coupling locking center differential, normally 50/50 torque distribution and up to 95% either axle when slipping occurs. Rear limited slip is optional. No low gearing.

Last updated: 2010-01-09 18:39

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Lincoln

Navigator Generation I 1998-2002 - Two wheel drive standard, Ford's Control Trac selectable all wheel drive optional (2H - Auto4wd - 4H - 4L). Similar to Expedition. Locking differential rear (opt.)

Navigator Generation II 2003-2006 - ?

Navigator Generation III 2007-... - selectable all wheel drive (2H - Auto4wd - 4H), no low range.

The Borg-Warner 1-speed torque-on-demand transfer case is a 2-piece magnesium design. The transfer case transfers engine power from the transmission to the front and rear axles. Under normal driving conditions, the unit is in All-Wheel Drive (AWD), but when desired, the operator may shift into X XXXXX XXXXX high (4H). The operator can switch between 2-Wheel Drive (2WD), AWD and Four-Wheel Drive (4WD) HIGH mode at any speed. The transfer case is equipped with an internal electromagnetic clutch and is shifted electronically. In AWD, the 4X4 control module varies the torque split between front and rear drivelines by controlling the transfer case clutch. Under most conditions, the 4X4 control module activates the transfer case clutch at a minimum duty cycle (percentage of time the clutch is turned on) which allows for a slight speed difference between the front and rear drivelines which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the 4X4 control module detects this slip condition and the duty cycle to the transfer case clutch is increased until the speed difference between front and rear drivelines is reduced. In this manner, the 4X4 control module can redirect engine torque to the front wheels when the rear wheels lose traction, yet still allow operation in the AWD mode on dry pavement. The unit is lubricated by a positive displacement fluid pump that channels fluid flow through holes in the rear output shaft.

http://www.justanswer.com/questions/22909-2008-lincoln-navigator-4x4

Last updated: 2010-01-09 18:39

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Mazda

323 GTX 1986-1992 - 1.6 4wd Turbo - full-time all wheel drive with planetary gear center differential, electrically lockable via a button on the console. Open differentials front and rear.
1.8 4wd - full-time all wheel drive with viscous-coupling limited slip planetary gear center differential, multi-plate type limited-slip differentials front and rear.

Before 1990: Torque split in normal conditions 50/50.
From 1990: Torque split in normal conditions 43/57 (for a rear-wheel-drive feel) could be varied to 60/40.

More information: http://www.mazdafun.com/bf%20drive%20train.htm

626 4wd - ?

6 MPS (MAZDASPEED6 in the U.S.) - "Active Torque Split" pro-active automatic all wheel drive. Normally front-wheel drive vehicle. Electronically controlled multiplate electromagnetic clutch transfers up to 100% of torque to the rear when needed. Limited-slip differential in the rear.

The MAZDASPEED6 with advanced AWD system analyzes real-time data on steering angle, yaw rate, lateral G-force and engine status to establish up-to-minute road surface conditions, and the vehicle's dynamic status. Normal, Sport, and Snow modes give the perfect amount of torque where it is most needed, and have a performance reaction that leaves conventional gear- or fluid-controlled systems in the dust. Front/rear torque distribution varies from 100/0 to 50/50.
Source: www.mazdausa.com

Last updated: 2010-02-01 0:19

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Mercedes

W124 4matic - Automatic all wheel drive. Normally rear wheel drive vehicle. Power is progressively transferred via multi-plate hydraulic transfer clutch to front wheels when slipping occurs. Torque distribution in this case is 65% to 35% rear to front. ABS sensors are used to detect wheelspin. If more traction is necessary, computer locks another clutch in rear axle. If brake pedal pressed, all clutches disengage to allow the ABS to work properly. On takeoff/acceleration the front axle normally engages, pro-actively, regardless whether wheel slip is detected or not.

ML - Full-time all wheel drive with 3 open differentials. 4ETS electronic traction control, that applies brakes to wheel, that is about to spin, thus transferring torque to wheels, that have traction. M-Class 4ETS kicks in up to about 36 MPH (60 km/h) and if engagement conditions are maintained beyond 60 km/h during acceleration, control is effective to up to 48 MPH (80 km/h).
Two-speed AWD variant of the Borg-Warner 44-06 transfer case. Button-operated low-range locks to 50/50 torque split. (2,64:1 low gear).

G-class 461 ...-1991 - Part-time all wheel drive. Manually lockable differentials in the front and rear axles.

G-class 463 1991-... - Full-time all wheel drive with 3 manually lockable differentials (buttons). Differentials lock after the vehicle has moved some distance. 2.16 low gear ratio.

Figure: MB G type 463 transfer case

W210 E-class - Full-time all wheel drive with 3 open differentials. Torque distribution 35% front / 65% rear via planetary gear. Electronic traction control applies brakes to the wheels that are about to spin and distributes torque from wheels that slip to the wheels with traction.

Last updated: 2010-02-15 21:12

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Mitsubishi

Lancer Evolution VII -

L200 (2004?) - Easy Select part-time all wheel drive. Front axle vacuum disconnect system. When in 2H mode, the right front driveshaft is disconnected from the front differential. The left and right front driveshafts are rotating freely in 2H mode.

Figure: Mitsubishi L200 all wheel drive system. Vacuum front axle disconnect system (1 - disconnected, 2 - connected)

Figure: Mitsubishi axle disconnect system

Figure: Rear differential lock

Pajero, Montero, Shogun 1982-1991, L200 - Part-time transmission. No center differential. Low gear. Some were equipped with limited slip differential in the rear.

Pajero II, Montero, Shogun 1991-2000, Pajero Pinin (1991-) - can have part-time all wheel drive (GL) or Super Select selectable all wheel drive system (GLX, GLS). Super Select works as a full-time all wheel drive when in 4H mode.

In case of a part-time transmission can have automatic hubs or a vacuum axle disconnect system. Super Select has a vacuum axle disconnect system.
Rear mechanical differential lock standard on GLS (100% lock, button activated).

Pajero III, Pajero IV - Super Select selectable all wheel drive system.

Last updated: 2010-02-15 22:14

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Nissan

Pathfinder I - Part-time all wheel drive.

Pathfinder (model years?) - All Mode automatic all wheel drive system - normally rear wheel drive, in AUTO mode front axle engages when rear wheels start to slip, power is variably distributed from 0:100 to 50:50 front to rear. In 2WD mode, the clutch is unlocked permanently. In 4H mode the tranfer clutch is permanently locked - power distribution 50:50.

Figure: All Mode all wheel drive system modes and scheme.

Patrol 160, GR Y60 ...-1998, Y61 1998-..., PickUp 1998-... - Part-time all wheel drive. LSD rear - standard, Locking differential - optional. 2,02:1 low gear.

Figure: Nissan Patrol GR transfer case

X-Trail - All Mode automatic all wheel drive system - normally front wheel drive vehicle, in AUTO mode rear axle engages when front wheels start to slip, power is variably distributed from 100:0 to 50:50 front to rear.

In 2WD mode, the clutch is unlocked permanently. However, even when in 2WD mode, front wheels can sometimes be engaged by electronic control unit, for example under heavy acceleration.

In LOCK mode the tranfer clutch is permanently locked - power distribution 50:50. If vehicle speed increases, the vehicle automatically goes to AUTO mode, then, when speed decreases, it switches back to LOCK. When transfer clutch oil is overheated, the vehicle goes into 2WD mode.

Figure: Nissan X-Trail All Mode 4wd system description

Last updated: 2010-02-15 22:39

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Opel/Vauxhall

Frontera (Isuzu Amigo) 1999 - Part-time all wheel drive. Lever-operated part-time two-speed transfer case with Neutral position. 4x4 button to engage the front axle (CAD). 2.05:1 low range gear. Front - corporate IFS with open differential. Rear - Dana 44 solid axle with limited slip.

Vectra - Automatic all wheel drive ?

Last updated: 2010-02-15 22:46

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Peugeot

205 Turbo 16 - Full-time all wheel drive. Viscous coupling locking planetary gear center differential (2). Automatically locking rear differential (3).

Figure: 205 Turbo 16 viscous coupling (2) locking planetary gear center differential (1)

405 4x4 GR and SR - ? Full-time all wheel drive. Planetary gear center differential.

Peugeot 405 4x4 Mi16 - ? Full-time all wheel drive. Viscous coupling (4) locking planetary gear center differential (3)

Boxer -

Peugeot commercial vehicles 4x4 conversion is performed by Automobile Dangel. Peugeot itself does not produce 4x4 vehicles.

Figure: Peugeot Boxer Dangel 4x4 conversion

Partner -

Figure: Peugeot Partner / Citroen Berlingo 4x4 Dangel conversion

? -

Figure: Unknown vehicle

Last updated: 2010-02-15 23:11

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Porsche

911 Carrera 4 - from 1989- three differential system using computer-controlled hydraulic clutches to help distribute power to the four wheels.

From 1994 - mechanical limited slip at rear, viscous coupling in the center.

From 1999 - viscous coupling just behind front differential, transferring from 5 to 40 % up front.

Figure: Porsche 911 Carrera 4 (unknown model year, probably 1994-1999) center differential with a multi-plate differential locking clutch. Appears to be a full-time all wheel drive system with torque distribution 31/69% front to rear.

959 - permanently locked multi-plate hydraulic clutch in the center. Unlocked only if turning at low speed, for example while parking. Torque distribution in this vehicle is adjusted even before wheelspin occurs. Gathering information from numerous sensors (i.e. g force sensor, accelerator pedal position, speed, and even turbo pressure) while accelerating, computer changes normal 40front/60back torque split, sending up yo 80% to the rear wheels, even if all four wheels are rotating with the same speed.

Last updated: 2010-02-15 23:24

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Renault

18 - ?

Scenic RX4 - Automatic all wheel drive. Normally front wheel drive vehicle. Torque transfer to the rear axle via viscous coupling.

Last updated: 2010-02-15 23:31

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Saab

9-3 Aero AWD 2007-... - Haldex XWD automatic all wheel drive. Haldex gen. III 2007-2008, Haldex gen. IV starting from 2008.

Last updated: 2010-01-09 18:39

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Seat

Seat Leon 4 (2000-2006), Seat Alhambra 4 (2001-2004) - Haldex Generation I automatic all wheel drive.

Last updated: 2010-02-19 22:41

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Skoda

Skoda Octavia I 4x4 (2001-2004) - Haldex Generation I automatic all wheel drive.

Figure: Skoda Octavia I all wheel drive

Figure: Haldex generation I coupling on Skoda Octavia 4x4

Figure: Skoda Octavia I power take-off to the rear axle

Figure: Skoda Octavia I 4x4 rear axle

Figure: Haldex clutch unit (2) insallation near the rear differential. Skoda Octavia.

Skoda Octavia II Combi 4x4 (2005-2009) - Haldex Generation ? automatic all wheel drive.

Skoda Octavia II Combi 4x4 Facelift (2009-...) - Haldex Generation IV automatic all wheel drive.

Last updated: 2010-02-19 22:48

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Subaru

"Models equipped with 5-speed manual transmission utilize a viscous-type locking center differential with torque distribution normally configured at a 50/50-split front-to-rear. If wheel speed differs between front and rear axles, the system helps distribute power to the wheels with the most traction.

Models equipped with 4-speed automatic transmission utilize an electronically controlled variable transfer clutch to distribute power to where traction is needed. Sensors monitor parameters such as wheel slippage, throttle position and braking, to help determine torque distribution and direct it to the wheels with optimum traction.

Models equipped with 5-speed automatic transmission utilize an electronically controlled variable transfer clutch in conjunction with a planetary-type center differential, and a viscous-type limited-slip rear differential. Torque distribution is normally configured at a performance-oriented rear-wheel-biased 45/55-split front-to-rear. Sensors monitor parameters such as wheel slippage, throttle position and braking to help determine torque distribution and direct it to the wheels with optimum traction.

Vehicles equipped with VDC (Vehicle Dynamics Control) electronic stability control also incorporate an all-wheel, all-speed traction control system (TCS) which senses a loss of traction and applies braking force to the slipping wheel or wheels as necessary to maintain vehicle motion."

Source: www.subaru.com

Impreza 1993-, Legacy 1989-, Legacy Outback 1997-, Forester 1997-

With manual transmission: Full-time all wheel drive with 50/50 torque split front-to-rear under normal conditions. Viscous coupling locking differential in the center inside the transaxle case, activates when wheels start to slip.

Figure: Subaru's manual transmission, center differential (10) and viscous coupling (11)

Figure: Subaru MT viscous coupling locking center differential

With 4-speed automatic transmission: Pro-active automatic all wheel drive with 90/10 torque split front-to-rear under normal conditions (60/40 on 2009 Subaru Forester). Electronically controlled hydraulic multi-plate transfer clutch installed instead of the center differential in the transaxle's tailshaft.

The hydraulic multi-plate transfer clutch ECU performs the following functions:
a) adjusts the hydraulic pressure according to the accelerator pedal position and the vehicle speed;
b) increases the hydraulic pressure when the gear shift lever at the position "1";
c) increases the hydraulic pressure when the front wheels start to slip (this function deactivates when the speed exceeds 60 km/h or when the accelerator pedal is released);
d) decreases the hydraulic pressure when the vehicle is turning;
e) cuts off the hydraulic pressure when ABS is activated.

Figure: Subaru's 4-speed automatic transmission (type MPT) and hydraulic multi-plate transfer clutch (23)

With 5-speed automatic transmission: Full-time all wheel drive with 45/55 torque split front-to-rear under normal conditions. Electronically controlled hydraulic multi-plate clutch installed in conjunction with the center planetary-type differential.

The hydraulic multi-plate clutch ECU performs the following functions:
a) adjusts the hydraulic pressure based on the produced torque and the road conditions;
b) adjusts the hydraulic pressure when the vehicle starts moving, based on the accelerator pedal position;
c) decreases the hydraulic pressure when the vehicle is turning (calculated by comparing the front and the rear's driveshafts speeds);
d) increases the hydraulic pressure when the front or the rear wheels start to slip;
e) cuts off the hydraulic pressure when ABS is activated;
f) decreases the hydraulic pressure when the brake pedal is pressed and when the accelerator pedal is released;
g) increases the hydraulic pressure when the gear shift lever at the position "1".

Figure: Subaru's 5-speed automatic transmission (type VTD), planetary-type center differential (23) and hydraulic multi-plate clutch (24)

Some models are equipped with viscous limited-slip rear differential.

Loyale 1994 -

Shift on the Fly: this refers to an less refined and effective, older Subaru 4x4 system that allowed the driver to engage the four wheel drive as the car was moving. Last used on the 1994 Loyale, but also used on older GL, DL, Subaru, Brat etc. Not currently used on any Subaru.

Libero ? - Part-time all wheel drive? Vacuum-actuated rear axle.

More information about Subaru all wheel drive

Subaru Forester 2009

"Thank you for contacting Subaru Canada, Inc.

The Forester does not have a Variable Torque Distribution (VTD) centre differential. For the 2009 model year, the Forester 2.5XT includes a Multi-plate Transfer (MPT) System that adjusts torque from 60/40 (F/R) to 50/50 (or anywhere in-between) depending on throttle input, road conditions and input from the Vehicle Dynamics Control (VDC) System. VDC operates like most electronic stability control (ESC) systems in that it can adjust engine output, adjust individual brake pressure and even front rear torque distribution to retain/regain vehicle stability.

It is not possible for the system defeat the role of the centre differential and thus torque output will always be split between the front and rear differential. Meaning, the system cannot direct 100% of power to a single wheel - whether it be with VTD or MPT.

We trust this information is helpful.

Sincerely,

Rosanne Kernerman
Bilingual Consumer Support Representative
After Sales
1-800-894-4212
www.subaru.ca"

Source

Last updated: 2010-02-19 23:00

6 Comments

Suzuki

Vitara - 1999-2005 - Part-time all wheel drive. Lever-operated two-speed part-time transfer case. 1.82:1 low gear. From 1999- new vacuum-actuated front axle disconnect, which eliminates the need of backing-up to disengage the the front hubs.
Corporate IFS open differential axle up front, corporate rear live axle equipped with limited slip.

Grand Vitara I - Part-time all wheel drive. Low gear.

Figure: Suzuki Grand Vitara transfer case

Suzuki Grand Vitara limited slip rear differential

Grand Vitara II - Full-time all wheel drive. Manually lockable center differential. Low gear.

Jimny - Part-time all wheel drive ?

Liana 4Grip - Automatic all wheel drive

Last updated: 2010-02-19 23:11

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Toyota

Celica -

RAV-4 (1994-2000), RAV-4 II (2001–2005), RAV-4 III (2005–present) - Sold with 2wd or full-time all wheel drive. Limited Slip Rear differential. Models with manual transmission also feature a center differential lock.

Figure: Toyota RAV4 II

4Runner Limited (1999) - Selectable all wheel drive system (full-time all wheel drive system with 4x2 capability). VF3AM transfer case. Lever-operated AWD, 4Hi, 4Lo (2,48:1), N modes. Corporate 8-inch IFS front axle is engaged using Toyota's ADD (Automatically Disconnected Differential), which is similar to other companies' CAD systems. Electro-mechanically operated rear differential lock (optional) in 8-inch solid axle.

Figure: Toyota's ADD (Automatically Disconnected Differential) in the front axle.

Land Cruiser FJ 100 - Full-time all wheel drive. Full-time two-speed four wheel drive system with manually (button) lockable differentials - center and rear (opt.) The case is similar to previous generation Land Cruisers

Figure: Toyota Land Cruiser 100 transfer case

Land Cruiser 80??? 1993 - Full-time all wheel drive system with viscous coupling locking center differential. Center differential locked when in low gear (2,49:1 ratio). Optional front and rear manually lockable differentials.

Land Cruiser 200 - Full-time all wheel drive system with dual range and 'yTorsen' (torque sensing) centre differential. Downhill Assist Control (DAC). Crawl control system (available on petrol V8 only).

Video: Toyota Land Cruiser 200 crawl control system operation.

Last updated: 2010-02-19 23:53

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Volkswagen

Golf Mk2 Syncro, Passat B2 Syncro (Quantum in the US), Sharan Syncro (1996-2001) - automatic all wheel drive system.

A viscous coupling installed instead of a center differential, with freewheel mechanism to disconnect the driven axle when braking. Open rear differential. Open front differential.

In normal conditions, this is a front wheel drive vehicle. In normal driving conditions 95% of torque transferred to front axle. Because viscous coupling is considered to be "slow" (some time is needed for silicone fluid to warm-up and solidify), 5% of torque is transferred to rear axle at all times to "pre-tension" the viscous coupling and reduce activation time. The coupling locks when slipping occurs and up to near 100% of torque is automatically transferred to rear axle. In on-road conditions the car will not move if one front wheel and one rear wheel lose traction.

The freewheel segment, installed inside the rear differential, lets rear wheels rotate faster than front wheels without locking the viscous coupling and preventing ABS from applying brakes to each wheel independently. Because of the freewheel, torque can be transferred to rear axle only when vehicle is moving forward. For all wheel drive to work when reversing, a vacuum-actuated "throttle control element" is installed on the differential case. This device locks the freewheel mechanism when in reverse gear. The freewheel mechanism unlocks when the gear shift lever is pushed to the right pass the 3rd gear. The freewheel is not unlocked immideately after leaving reverse gear on purpose - this is to prevent the freewheel from cycling from locked to unlocked if the car is stuck and driver is trying to rock the car by changing from 1st to reverse and back.

Disadvantages of this all wheel drive system are related to actuation time of the viscous coupling. 1: When cornering under acceleration on a slippery surface, rear axle is engaged with delay causing sudden change in the car's behaviour (from understeer to oversteer). 2: When starting on a sandy surface, front wheels can dig into the sand before all wheel drive is engaged.

Figure: Volkswagen Golf MkII Syncro

Figure: Volkswagen Golf MkII Syncro power transfer to the rear axle

Figure: Volkswagen Golf MkII Syncro rear axle gear unit with visco-clutch, free-wheel unit, and bevel gear differential.

Figure: Volkswagen Golf Mk2 Syncro freewheeling mechanism(12)

Figure: Volkswagen Golf Mk2 Syncro throttle control element(15)

Passat B6 Syncro (1997-1999) / 4motion (1999-2005) - Torsen-based full-time all wheel drive. See Quattro generation IV.

Passat B7 4motion (2005-...) - Haldex Generation II automatic all wheel drive. Haldex Generation IV automatic all wheel drive since 2007.

Golf IV 4motion, Bora/Jetta 4motion, Beetle Rsi, Sharan 4motion (1999-...) - Haldex Generation I automatic all wheel drive. Haldex Generation II automatic all wheel drive since 2002. Haldex Generation IV automatic all wheel drive since 2007.

Tiguan 4motion (2007-...) - Haldex Generation IV automatic all wheel drive.

T4 Syncro - Automatic all wheel drive system with torque transfer to the rear axle via viscous coupling. Manually locking rear differential.

T4 4motion - Haldex automatic all wheel drive. Manually locking rear differential.

Iltis -

Last updated: 2010-02-20 0:14

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Volvo

850 AWD - Automatic all wheel drive, torque transfer to rear axle via viscous coupling when front wheels slip, electronic traction control on front wheels, limited slip rear differential.

Figure: Volvo 850 viscous coupling and disconnect unit (what is a disconnect unit?)

V70 AWD (1997-2002), V70 Cross Country (2000-2002), XC70 (2002) - Automatic all wheel drive, torque transfer to rear axle via viscous coupling when front wheels slip, electronic traction control on front wheels (TRACS - Volvo's brand of traction control). TRACS system works on speeds up to 40kph(25mph).

Volvo S60 AWD (2002) - Haldex Generation I automatic all wheel drive.

Volvo S60 AWD (2003-...),
Volvo V70 AWD (2003-...),
Volvo XC 70 (2003-...),
Volvo S60R AWD,
Volvo V70R AWD - Haldex Generation II automatic all wheel drive.

Volvo XC 90 (2002-...) - Haldex Generation II automatic all wheel drive.

Last updated: 2010-02-20 0:05

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