Hauling Or Handling?

Cross/utility vehicles and SUVs present a challenge for shock absorber and damper makers because they are sold as passenger vehicles that also can be used as pack mules.

Designing a shock absorber for load-handling isn't troublesome, as millions of pickup trucks prove. Pickups can handle heavy loads just fine, but because their shocks are designed largely for that purpose, there's usually a ride-quality price to be paid when driving around with nothing in the bed.

But many CUVS and SUVs are luxury or near-luxury models — and their buyers expect ride and handling refinement that far exceeds that of an everyday pickup. How, then, to satisfy these divergent needs?

ZF Sachs Automotive of America, the maker of shock absorbers and dampers that is part of giant supplier ZF Friedrichshafen AG, says it has the answer with its Nivomat shock.

Nivomat is a monotube shock absorber (typically used only at each rear corner in concert with a conventional spring) that incorporates a unique self-leveling feature.

Nivomat's developers, including Product Engineering Manager Uwe Grasse, say the unique and versatile shock is hardly a new development. Earlier generations of Nivomat (broadly translated from French as “automatic leveling”), date as far back as 1967 and employed the same design principle, which uses the vehicle's body movement as the “pump” to generate pressure that provides the self-leveling performance.

When the vehicle body, laden with the extra weight of a load, starts to move up and down as bumps and other road irregularities are encountered, the shock's piston rod (which is attached to the wheel) draws oil from a low-pressure reservoir and shoves it through a valve into a second chamber.

As the oil is pumped into the high-pressure reservoir, it raises the piston rod to a predetermined ride height, at which point a height regulator triggers valves that allow a bypass to divert the oil from the high-pressure chamber.

The result: Nivomat pumps itself up to a consistent ride height regardless of how much weight rests on the rear of the vehicle.

Grasse says a competitive compressed-air load-leveling shock-absorber system that provides similar performance typically weighs around 16 lbs. (7.5 kg) more than a pair of Nivomat shocks, and requires 14 individual components vs. Nivomat's two parts — the shocks themselves.

But Nivomat's best feature, says Julio C. Caspari, president of ZF Sachs' NAFTA chassis division, is its safety benefit. By keeping ride height and ride frequency consistent regardless of load, Nivomat shocks make a loaded vehicle safer-handling, says Caspari.

“Nivomat is not a cheap part,” says Ronald M. Gesguire, senior vice president, sales and engineering-suspension. “But the benefits you get pay for it.”

He says Nivomat typically is about $300 to the retail customer, but that's markedly less than the cost of a full-blown air suspension, with its dedicated compressor and demonstrated warranty exposure.

Nivomat is available or standard on a raft of vehicles that represent a cross-section of just about every major market segment, from passenger cars such as Cadillac's new CTS and Chrysler's ubiquitous minivans to genuine SUVs that include the Chevrolet Suburban and Tahoe.

With the U.S. market skewing toward multipurpose SUVs and CUVs, company execs say Nivomat may be the ideal solution for vehicles in which customers expect load-hauling capability on rare occasion — but outstanding dynamics all the time.

Grasse and Caspari admit the pickup would be the dream application for Nivomat. But because of the much higher payloads and gross vehicle weight assumed for pickups, Nivomat's monotube design is not yet capable of handling heavy loads pickups are built to carry.

Grasse says ZF Sachs engineers are working, however, to develop a high-capacity version of Nivomat that would be suitable for pickups.