Benefits of a Networked Chassis

Despite Vast Improvements in Computing power and electro-hydraulics, advanced chassis and drivetrain systems only will function at their full potential if they manage a vehicle's dynamic forces in a controlled and coordinated manner.

At least that's the thinking of Germany's ZF Friedrichshafen AG, which recently held a technology clinic at Michelin SA's proving grounds in Laurens, SC, to showcase what its latest products are capable of when properly networked.

Offerings range from the supplier's second-generation, 6 HP 28 6-speed automatic transmission in the BMW 3-Series and Audi A5, to a pint-sized Formula 1 clutch assembly that weighs about 1 lb. (0.5 kg) and costs as much as a small car.

A skidpad provides ample room to experience the added agility and control of ZF's new Vector Drive (VD) rear axle in the BMW X6 cross/utility vehicle, as well as show how the optional load-leveling Nivomat dampers on the Cadillac CTS can counter the added inertia of more than 700 lbs. (318 kg) of cargo.

But it is a BMW 5-Series wagon that serves up the most impressive innovation: An updated version of ZF's Intelligent Wheel Dynamics (IWD) system.

Introduced in 2005 on the ZF/Karmann GmbH Sport Utility Cabrio (SUC) concept, the technology links together active suspension, steering and power-transfer systems for optimal control.

The wagon's power is sent through a ZF 6-speed automatic to a prototype all-wheel-drive transfer case. A torque-vectoring rear differential proportions power from side to side, helping rotate the car in corners and raising the handling threshold before the electronic stability control (ESC) intervenes.

The suspension has been upgraded with ZF's electronic Continuous Damping Control shocks.

BMW's ZF-sourced active steering system, which varies the steering ratio at low speeds for easier maneuvering, remains on the car, as does the supplier's Active Roll Stabilization (ARS), which stiffens the anti-roll bars in corners for flat handling and decouples them for more comfort.

However, electro-mechanical actuators replace BMW's hydraulic ARS system so the feature can be deactivated at will. Electronic ARS also can be bundled more easily with electric power steering, yet draws only one-fifth the power of EPS.

The IWD 5-Series is all business, exhibiting exemplary control for a large AWD wagon on an autocross course.

Turn-in response is crisp, and the body stays amazingly flat during high-speed maneuvers. The VD axle makes short work of slalom runs, keeping the ESC at bay and pivoting the rear end around with the effect of 4-wheel steering.

But with the active steering, VD and ARS systems disabled, traversing the same course becomes much harder. Sharp bends are plowed through, rather than rotated around. Even though the average speed is much slower than before, the excessive body motions cause the ESC to go into overdrive as the electronics sense an impending spin and pinch the brakes to get the car back on line.

No active steering also means the car now waddles through low-speed switchbacks at what feels like a snail's pace.

The production outlook for IWD is uncertain, but the technology seems like a no-brainer for performance cars and people movers alike.

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