Need an IRS ASAP?

Look what Ford Motor Co. has started. With the addition of independent rear suspensions (IRS) on Ford Explorer/Mercury Mountaineer and the upcoming 2003 Lincoln Navigator/Ford Expedition, surely every SUV producer will clamor for IRS.

That appears to be the hope of at least two prominent automotive suppliers that are ready to take IRS to an even larger audience.

Both ArvinMeritor Inc. and American Axle & Mfg. have invested a fair amount of cash and engineering power in producing drivable prototypes that are being shopped to potential customers.

Their unmistakable prime target is General Motors Corp., North America's No.1 SUV producer. All GM SUVs and pickups have solid rear axles.

ArvinMeritor showed its unique IRS module to Ward's editors just before presenting it to the first of its current four potential OE customers, all of who presently make fullsize ladder-frame SUVs derived from pickup-truck architectures. So far, ArvinMeritor has spent $500,000 and 10 months on the program, says Robert Carlstedt, ArvinMeritor's vice president, suspension module engineering.

Although the IRS module was installed on a GMC Yukon Denali, ArvinMeritor says the concept applies to any auto maker that would like to upgrade the dynamic abilities of ladder-frame, solid-axle vehicles — or could use a turnkey IRS module for a unibody vehicle, perhaps, as a way to quickly offer all-wheel drive for an existing front-drive-only platform.

In city traffic, the Yukon Denali prototype handled well, although the company concedes that it needs additional roll and damping adjustment. It was difficult, however, to discern a vast improvement in handling, given that the existing GMT800 is much more refined than GM's old fullsize pickups.

ArvinMeritor engineers insist the IRS module program wasn't done to prove they could take over an auto maker's suspension-development competency. “I don't think they (OEMs) expect us to design suspensions,” says Doyle Downey, modular suspension systems sales manager at ArvinMeritor. “But they've said, ‘We want to see a supplier who understands suspensions.’” ArvinMeritor already produces coil springs, stabilizer bars, torsion bars, struts and links for rear suspensions.

ArvinMeritor engineers call the prototype IRS module's layout “tri-link SLA” because it employs three bottom links at each rear wheel (and a single A-arm shaped top attachment point) in what mimics a short/long-arm suspension design. There are two lower longitudinal links and a trailing link attached to the frame, with a top attachment point via the A-shaped link.

Carlstedt says the development goal was for the entire IRS module to weigh no more than 10% more than the solid-axle suspension it replaces. Another goal was to keep the module cost within 10% of the current suspension.

The ArvinMeritor IRS could be a bolt-in replacement for the current rear suspension of GM's fullsize pickups and SUVs, but the company has set its sights on OE business rather than the aftermarket.

If ArvinMeritor landed a GM contract for IRS, the company could assemble the modules wherever the customer wants — perhaps even at an ArvinMeritor plant that opened last year in Detroit. The supplier has even devised a manufacturing plan that melds seamlessly with GM's current truck assembly lines.

The complete module would integrate parts from multiple suppliers and could include the axles and rear differentials manufactured by other companies. ArvinMeritor produces heavy axles for commercial vehicles but has no interest in doing axles for light vehicles, Carlstedt says.

And that is good news to American Axle (AAM), which produces the axles for GM pickups and says it is guaranteed the axle business for GM's next-generation fullsize pickups, whether an IRS is used or not.

If GM opts for an IRS, AAM doesn't want to be left out, so the former GM affiliate has installed its own IRS on four prototype vehicles — a 2002 Cadillac Escalade, a 2002 GMC Envoy, a Jeep Grand Cherokee and a Chrysler 300M. The 300M was chosen to demonstrate the conversion of a front-drive sedan to all-wheel drive without changing the vehicle architecture.

Like the ArvinMeritor module, AAM's I-Ride setup can be a bolt-in replacement for the current suspension on GM's fullsize pickups and SUVs. Still, AAM has its eye on OE rather than the aftermarket. I-Ride consists of a cast aluminum monocoque rear module structure, a PowerLite aluminum rear independent axle and the new AAM Powerlite aluminum power transfer unit.

Ronald Schoenbach, AAM director of chassis engineering, says OEM customers have been very responsive to I-Ride. “They acknowledge that we're ahead of the trends with our design,” he says. “We know we're not first with an IRS, but we've added a level of refinement to it.”

The Escalade prototype, interestingly, has the capability of incorporating rear-wheel steering, a product Delphi Corp. has sold to GM for fullsize pickups and SUVs. But AAM isn't working exclusively with Delphi on rear-steer as part of I-Ride; the axle maker also is working with steering specialists TRW Automotive and Aisin Seiki Co. Ltd.

Likewise, ArvinMeritor's IRS module has rear-steer capability, thanks to steering technology from SKF Automotive Div.