Wednesday, November 02, 2005


Text from Volkswagen of America.
All-Wheel Drive, All the Time

LAS VEGAS, Nev. – Volkswagen’s GTI essentially created and defined the performance sports hatch/sports coupe segment that today is populated with the likes of the Mazda3, Chevy Cobalt, Honda Civic and Ford Focus. That original GTI was the first pocket rocket, the mating of a powerful engine to a lightweight sedan chassis. In 2004 VW upped the ante with the R32, one of the most powerful VW models to date, thanks to a new and highly responsive 240-bhp 3.2-liter V6 engine. With 20-percent more power and 20-percent more tire-smoking torque lurking under the hood, Volkswagen engineers realized that it was time to not only talk the torque but to split the torque…to both axles, instead of leaving it all up front.

Enter 4MOTION, VW’s all-wheel-drive system which ensures that every bit of power is efficiently distributed to all four tire patches, assisting the R32 in the areas of stabilization, traction and balanced handling. Fun to drive? You bet.

Before delving too deeply into 4MOTION, understand that there are two different versions, one for VW models equipped with longitudinal drivetrains, such as the Phaeton and Touareg, and another for those VW models with transverse engines, including Jetta and Passat. Phaeton and Touareg models use a Torsen center differential to control and deliver power to all four wheels. However, the transverse drivers are equipped with a high-performance Haldex clutch at the rear axle to accomplish the same task. And it is the latter system that we will concentrate on here. This is actually the second-generation 4MOTION; an earlier version was introduced on the Golf in some markets (but not the U.S.) in 1998. This new-generation all-wheel-drive system has been improved in many aspects. For example, the Haldex clutch unit mounted directly on the rear axle is now significantly more compact.

The most important technical element of 4MOTION is the latest generation wet-running (oil bath) Haldex multi-disc clutch. Compared to a straightforward mechanical Torsen® differential, the Haldex unit offers the significant advantage that it can be electronically controlled. As a result, it integrates perfectly with the Anti-lock Brake System (ABS), traction control Anti-Slip Regulation (ASR), the Electronic Differential Lock (EDL), and the Electronic Stabilization Program (ESP).

As soon as there’s any difference in the rotation speeds of the front and rear axles, two pumps located within the multi-disc clutch are activated. These build up pressure in the transmission unit and thereby “link together” the two axles. They only take effect when the input and output shafts of the transmission unit are no longer turning at the same speed because only then is torque splitting necessary.

Altering the pressure exerted on the clutch discs can vary the amount of torque transmitted. This makes it possible to control the power flow between the front and rear wheels. The transmission unit performs infinitely variable torque control from zero up to full transmission – a 50:50 split of the propulsion power between the front and rear wheels.

When the car is driving straight ahead and there’s no difference in grip between the wheels, 90 percent of the power is sent to the front axle and 10 percent to the rear. The only thing the driver really notices is that any VW model equipped with 4MOTION retains neutral handling characteristics and stays on course in practically any situation.

The Haldex coupling is mounted on the rear axle differential and is driven by the drive shaft. The electronic control unit for the Haldex clutch unit gets all the important drive and engine information via the CAN (Controller Area Network) bus. This includes signals from the wheel sensors, the ABS and ESP as well as information about the accelerator pedal position and engine revs. This data provides the engine control module with all the information it needs on road speed, cornering, coasting or traction mode, allowing the system to continually monitor and regulate the level of hydraulic pressure to respond optimally to any driving condition.

Commands from the electronic control unit are carried out very rapidly by the Haldex unit. Full pressure is applied after a rotation angle of only 45 degrees of the first revolution after the Haldex receives an electronic signal. This generates the corresponding torque at the rear axle.

What about side-to-side slippage? This is when the Electronic Differential Lock comes into action to control traction. Think of this as ABS in reverse because EDL uses the same sensors and components as the ABS but to control “acceleration” instead of “braking” slip.

The speed sensors at each wheel continually send information to the ABS control module. When there is a difference in wheel speeds, the EDL function applies the brakes to the wheel that is spinning to control slip. When brakes are applied to the wheel that is spinning, power will automatically be sent through the differential to the wheel that has traction. For example, if the vehicle is on a patch of ice and only one wheel has traction, EDL will pump the brakes of the three wheels that are spinning.

Some of the system’s important characteristics include compatibility with different size tires, quick response and no strain on the multi-plate clutch when parking and maneuvering.

Traction off the line is aided by the Haldex coupling, which directs power to the rear wheels when it detects the front pair slipping.

You’ll also experience the benefits of 4MOTION the moment you attempt to accelerate on wet or slippery pavement. In a front-wheel-drive vehicle, the car will attempt to spin its front wheels. But before it can do this, the car’s traction control system will intervene, applying the brakes and adjusting the throttle opening. The net effect is that you’ll accelerate at a rather modest rate. 4MOTION response is decidedly different.

Transferring torque to those tires with the most traction results in dramatically quicker acceleration. The only time the traction control will intrude significantly is on an extremely slippery surface such as ice.

Drivers will really appreciate the precise manner in which a 4MOTION-equipped VW corners and steers. Torque steer is eliminated. Absolutely gone. The first time you accelerate hard through an uphill hairpin bend with a lot of steering cranked on and experience the ease with which the VW model grips the pavement. With 4MOTION, power can be transmitted variably to all four wheels using electronic control. This means each wheel always gets the appropriate amount of power for the available grip.

Founded in 1955, Volkswagen of America, Inc. is headquartered in Auburn Hills, Michigan. It is a subsidiary of Volkswagen AG, headquartered in Wolfsburg, Germany. Volkswagen is one of the world’s largest producers of passenger cars and Europe’s largest automaker. Volkswagen of America and its affiliates employ approximately 3,000 people in the United States and are responsible for the sale and service of Audi, Bentley, and Volkswagen products through retail networks comprising in total more than 900 independent U.S. dealers.

"Volkswagen" and "4MOTION" are registered trademarks of Volkswagen AG. "DSG" is a trademark of Volkswagen AG. All other trademarks used in this document are the property of their respective owners.


Anonymous Anonymous said...

VW really should consider making 4Motion available in most (or all) of its models. This is almost like having ABS tech in the 80's, by the middle 90's ABS was standard in almost all cars. VW should try to make 4motion standard in all cars/vans sold NOW (get a head start vs Japanese competition). It already has the technology pretty much figured out, the competitioon still haven't perfected theirs, so VW should market theirs as much as possible before a cheaper Japanese copy gets put in all Hondas and Toyotas (then it might as well be 4motion corolla).

Sat. Nov. 12, 10:48:00 p.m.  
Blogger prolix said...

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Sun. Oct. 09, 11:00:00 p.m.  

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