10 GEARS August 2010

by Pete Huschermembers.atra.com

www.atra.com

Keep Those Tranny’s rollingQuattro and 4Motion: Volkswagen Group’s Answer to All-Wheel Drive

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The Volkswagen Group has been

developing four-wheel drive

vehicles sincebefore the second World War, where

they developed the Kubelwagen, Schwimmwagen, Kommandeurwa-gen (all 4x4 ve-

hicles), and even a four wheel drive

Volkswagen Beetle. In this issue of Keep Those Tranny’s Rolling, we’re going to look at the AWD systems offered

by the Volkswagen Group.One of the most commonly known

AWD systems from Europe is from the Volkswagen Group, which manufac-tures Audi and Volkswagen vehicles. The AWD system used by Audi is known as the Quattro system and the AWD system used by Volkswagen is known as the 4motion system.

The Volkswagen Group has been developing four-wheel drive vehicles since before the second World War, where they developed the Kubelwagen, Schwimmwagen, Kommandeurwagen (all 4x4 vehicles), and even a four wheel drive Volkswagen Beetle.

The Volkswagen Iltis, which was designed in the 1970s for the German military, used an early form of four

wheel drive that would later become known as Volkswagen’s Quattro sys-tem.

The Volkswagen Group uses two different types of AWD systems: the longitudinal system and the transverse system, depending upon engine and transmission orientation.

Longitudinal SystemsThe early Quattro systems, starting

with the 1978 Audi 80, were permanent, four wheel drive systems, equipped with a manually lockable, open center

differential (more commonly known as a transfer case or power take-off unit), a manually lockable, open rear differ-ential, and a non-locking, open front differential. These were known as first generation systems.

In late 1987, Audi replaced the manually-locking, open center differ-ential with a Torsen Type 2 (short for torque sensing) center differential (fig-ure 1). The Torsen carrier assembly works basically the same as a limited slip differential: It distributes the torque difference between the output shaft with the least amount of traction avail-able and the output shaft with the most traction available.

GEARS August 2010 11

Figure 1: Quattro’s Torsen Centre Differential

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The Torsen coupler supports a stat-ic torque ratio split of 50% to the front axle and 50% to the rear axle, and is capable of a torque ratio split of 33% to the front axle and 67% to the rear axle under aggressive driving conditions.

These were permanent four wheel drive systems, equipped with a Torsen center differential, a manually lock-able, open rear differential, and a non-locking, open front differential. This all wheel drive system is controlled by the ABS and is known as a second genera-tion Quattro system.

In 1990, Audi replaced the locking rear differential with a Torsen type rear differential. A planetary set was added to the Torsen center differential for all V8 Audi Quattros with automatic trans-missions. Audi Quattros with manual transmissions came equipped with a Torsen center differential and a Torsen-type rear differential. Both models con-tinued to use the open front differential. This version of the Quattro system was referred to as third generation.

In 1995, Audi replaced the manu-ally locking, open differentials with a newly designed Electronic Differential Lock (EDL) open differential system. The EDL system detects wheel slip by monitoring the ABS wheel speed sensors, and then gradually applies the brakes to the slipping wheel, allowing torque to be transferred to the opposite wheel.

This forth generation system con-tinued to use the Torsen T2 center differential. This system was also intro-duced on the 1995 Volkswagen Passat, where it was initially referred to as the syncro system. It was finally renamed the 4Motion system. Volkswagen con-tinues to use the 4Motion name for its all wheel drive systems. This system is referred to as the fourth generation of the Quattro system.

Beginning in 1996, Audi replaced the Torsen T2 center differential with a new design Torsen T3 center differen-tial. The Torsen T3 center differential combines a planetary set with a Torsen differential. Unlike the Torsen T2 car-rier, the Torsen T3 carrier torque split is closer to 40% to the front axle and 60% to the rear axle. With 60% of the torque being sent to the rear axle, the Torsen T3 system provides a rear wheel drive

type feel.The Torsen T3 system continues

to use an open rear differential with Electronic Differential Lock, and an open front differential also equipped with the EDL system. The Torsen T3 system is referred to as the fifth genera-tion of the Quattro system.

Audi’s sixth generation Quattro system is known as the Quattro Torque Vectoring System (figure 2). The torque vectoring system was built by ZF Manufacturing under the name Vector Drive, and is being offered on the Audi

A4, A5, A6, Q7, and Q5.The Quattro Vectoring System still

uses the Torsen T3 carrier in the center differential. The open rear differential with the EDL system has been replaced with an electronically controlled Active Sport Differential. This new system continues to use an open front differ-ential equipped with the EDL system.

Transverse SystemsThe Volkswagen Group considered

adding an all wheel drive system to their A-platform cars back in 1974. But

Figure 2: Quattro’s Torque Vectoring System

12 GEARS August 2010

Quattro and 4Motion Continued

it didn’t seem to materialize until the second generation of A-platform cars in the mid-1980s.

The A-platform cars had a trans-versely mounted engine and transmis-sion with a power take-off unit (PTU) mounted to the side of the transmission. The purpose of the PTU was to deliver driving torque to the front and rear axles. The rear drive axle was equipped with a viscous coupler to minimize driveline windup or binding.

This viscous coupler type all-wheel drive system was found on the Golf, Jetta, Vanagon, Passat, and Eurovan. The viscous coupler system was only used on Volkswagens; never on any Audi vehicles. This early system was known as the syncro system.

The Haldex SystemIn 1998, Volkswagen replaced the

viscous coupler system with the Haldex Traction LSC system, which uses an electronically controlled, hydraulic, limited-slip coupler in place of the vis-cous coupler (figure 3).

The Haldex Traction LSC system was an option on the Audi A3, S3, and TT models under the Quattro name. It

Haldex AWD

systems are

currently being

used by several

automotive manu-

facturers such as

the Volkswagen

Group, Volvo,

Saab, Land Rover,

Bugatti, General

Motors, and Ford

Motor Co.

was also available in the Volkswagen Golf, Golf R35, Jetta, Sharon, Passat,

and Transporter T5 models under the 4Motion name.

Haldex AWD systems are current-ly being used by several automotive manufacturers such as the Volkswagen Group, Volvo, Saab, Land Rover, Bugatti, General Motors, and Ford Motor Co.

The Haldex Traction LSC sys-tem is controlled by the Haldex ECU (figures 4 and 5). The Haldex ECU uses information from the ABS control module to control the AWD system. This system attempts to engage the rear drive axle when it detects front wheel slip.

The Haldex ECU engages and dis-engages the Haldex clutch as needed to allow the ABS system to operate prop-erly, and to prevent driveline binding during tight turns. The mechanical front and rear open differentials were replaced with front and rear, electronically con-trolled, open differentials (EDL).

This system uses the ABS and sta-bility ride system to control the AWD system by applying the brakes to slow the wheel with the least amount of trac-tion.

Figure 3: Haldex LSC System Components

14 GEARS August 2010

Figure 4: Haldex’s Traction LCS System

Diagnosing the AWD Systems

Diagnosing the Audi and Volkswagen AWD system is pretty straightforward. The AWD systems are controlled by the ABS control mod-ule and Haldex ECU (if equipped). Diagnosing the ABS and Haldex system will require using a VAG or compatible scan tool that’s capable of accessing the ABS control module and the Haldex ECU.

Once you have access to the ABS control module and the Haldex ECU:

• Retrieve and document all codes stored in the both modules.

• Clear all codes from the ABS control module and Haldex ECU, and recheck the AWD system operation.

• IfABSorHaldexsystem codes return, diagnose and repair these codes as needed.

• Ifnodiagnosticcodesare present and you continue to experience AWD system problems, inspect the AWD

components.

Remember to check the basics: check and compare tire sizes, circum-

ferences, and tire pressures. If every-thing looks good, you may have a mechanical problem with the center, rear, or front differentials. Inspect andrepair as needed.

Well, there you have it: an inside look at what makes the Quattro and 4Motion AWD systems operate. With a better understanding of how these

AWD systems operate, you should have no problem keeping those tranny’s and AWD systems rolling.

Figure 5: The Haldex ECU

Quattro and 4Motion Continued