TV Ready for Prime Time
By Tom Murphy Ward's AutoWorld, Mar 1, 2008 12:00 PM

The wonders of torque vectoring have been apparent since the Acura RL launched as an '05 model with Honda Motor Co. Ltd.'s Super Handling All-Wheel Drive system.

But on a frozen patch of Michigan's Upper Peninsula tundra, the improved handling, chassis dynamics and all-around drivability are even more evident, and extremely tunable, too.

Magna Powertrain USA Inc. spent two weeks recently demonstrating its drivetrain capabilities for customers and media at a winter test track near Brimley, and the crowning prototype everyone wanted to drive was an AWD Infiniti G35x sedan, whose standard open differential was replaced with Magna's torque vectoring rear-drive axle module.

Later this year, Magna will supply its TV technology for the Audi A4 and A5 as optional equipment, hooked up to Audi's well-regarded Quattro AWD system. In 2009, the A6 and A8 are in line for it. By then, all four vehicles will share a common architecture.

BMW AG also will bring TV to market this year on the all-new X6 cross/utility vehicle. That system comes from transmission specialist ZF Friedrichshafen AG.

Most AWD and 4-wheel-drive systems allow torque to be transferred between the front and rear axles, depending on which one needs the most traction.

But electronically enabled torque vectoring allows wheels on the same axle to transfer power from side to side. The system can add torque to one wheel, while subtracting it from the other, creating opposing vectors causing the vehicle to rotate with less steering effort.

The G35 demo vehicle is equipped with a switch allowing the driver to experience various levels of vectoring. In standard open differential mode, the car tends to understeer, forcing a driver wanting to change lanes quickly to apply more steering and throttle inputs to get the back end to come around. The result is a lot of slipping and sliding.

In TV mode, the G35 undergoes an amazing transformation, as four different settings demonstrate the possibilities.

In basic mode, the torque-vectoring function is dedicated to keeping the vehicle on its proper course, especially during off-throttle maneuvers.

In sport mode, the tuning is more aggressive during throttle-on cornering, and there is virtually no correction during off-throttle maneuvers. It's much easier to bring the back end around.

Add power to an outside wheel during hard cornering, and the effect on a vehicle's deportment is remarkable.

The last two demonstration modes are parlor tricks, rather than intended for serial production.

Todd Ekonen, product architect-transverse systems at Magna Powertrain, refers to one as “swivel” mode, turning the car into a chair on castors, like a '79 Trans Am doing doughnuts in a snowy mall parking lot. At the opposite end is “stability” mode, intended solely to keep the vehicle steady by creating counterbalancing torque “moments” on certain axles.

Switch from “swivel” to “stability” mode and the car instantly transforms from nervous and eager-to-oversteer to calm and surefooted.

“With torque vectoring, the car feels more crisp all the time,” Ekonen says. “The harder you drive, the better it feels.”

He considers rear-drive sport sedans and coupes as ideal applications for torque vectoring because of the massive handling improvements that are feasible.

On a high-friction surface, the G35's sport vectoring system makes cornering simple — and entertaining. Steering feels quicker, without alterations to the steering system.

Other suppliers are jumping into the TV market as well.

Working with ZF on this year's X6 vectoring program is GKN Driveline, which supplies the TV hardware units. ZF is responsible for final assembly, the drive axle, planetary gear sets, electric motors and electronic controller.

Beyond the BMW application, ZF and GKN intend to market the rear-axle TV technology to other auto makers under the name VectorDrive. The basic system includes two torque-vectoring units flanged to the final drive and two electric motors. An electronic controller governs the motors.

OEMs are extremely interested in TV for future vehicles, especially as AWD cars and CUVs replace rear-drive SUVs, says Paul Olexa, vice president-driveline sales and marketing for ZF Group North America.

Although the Honda system works well in the Acura RL, Olexa says Honda's TV function only works with the throttle open and not during coasting.

The ZF system — as well as Magna's — works under both open- and closed-throttle conditions. “We can transfer torque and speed to a wheel that needs it,” Olexa says.

Electronic limited-slip differentials, which are becoming more popular, also are capable of transferring torque from wheel to wheel, but only under load. “If you take your foot off the throttle, you can upset the handling of the car,” Olexa says.

Another key player in the emerging TV market is BorgWarner Inc. While ZF and Magna's initial launches are focused on rear-drive architectures, BorgWarner is looking more aggressively at TV applications among front-wheel-drive vehicle platforms, says John Barlage, product business director-advanced products at BorgWarner's TorqTransfer Systems division.

BorgWarner's electronic torque-vectoring axle (ETVA) uses electromagnetic pressure to actuate the clutch within the differential, which Barlage considers a less expensive alternative to the pumps or electric motors necessary for the other systems.

The supplier delivers rear-drive axle modules for the Honda Pilot CUV and Ridgeline pickup — both derived from a front-drive architecture for an AWD application.

Neither the Ridgeline nor Pilot employ TV, but both rear-axle modules are capable of adding it, Barlage says.

Without providing details, Barlage says BorgWarner's TV technology is “very competitive” when priced against the ZF and Magna solutions. He says the market has grown since the mid-1990s, when the first form of torque vectoring appeared on the low-volume Mitsubishi Lancer Evolution AWD rally car.

In addition to the RL, Barlage says the Acura RDX and MDX CUVs offer limited vectoring capability as well, while all three vehicles share the same rear-axle module.

“They achieve economies of scale,” Barlage says of Honda. “If you look at the market data, there's an increase in torque-vectoring activity. There's an explosion in volumes now with Audi and BMW coming on line.”

He says BorgWarner is talking about TV programs with “just about every” OEM. “I think the Acura activity has really stirred up the market a bit,” Barlage says. “Everyone is thinking about how to differentiate themselves in the marketplace.”

Despite the technical differences between each supplier's TV solution, all three are capable of channeling about 20% more torque to one wheel than the other.

Audi to Quell Understeer With New Differential http://subscribers.wardsauto.com/ar/audi_new_differential