CHANGCHUN, China – It’s been 10 years since auto makers began upgrading some of their suspension systems with advanced dampers using magnetorheological fluid to mitigate body roll and allow a vehicle to respond within milliseconds to potholes, uneven pavement and sudden changes of direction.
A Virginia Tech professor who has studied the fluid extensively and worked previously for the company that popularized it in performance cars predicts that within 15 years vehicles using MR-based adaptive suspensions will be common in the mature markets, even for high-volume vehicles such as the Toyota Camry or Chevrolet Malibu.
In that timeframe, about half of all automotive dampers will rely on MR fluid, predicts Mehdi Ahmadian, professor of mechanical engineering at Virginia Tech. He says at least a dozen vehicle platforms globally use MR-based suspension systems.
“I know that number is growing very fast,” Ahmadian says here at the International Conference on Advanced Vehicle Technology and Integration. “Auto manufacturers are finding a way to put it into their lower-priced vehicles from the premium vehicles.”
Lord Corp., based in Cary, NC, pioneered the technology for automotive suspensions with the launch of the ’02 Cadillac Seville STS and, soon after, the Chevrolet Corvette.
Several other vehicles have followed suit, including the Ferrari 599 GTB, Audi R8, Buick Lucerne, Acura MDX, Cadillac Escalade and Cadillac CTS-V.
The barrier to entry for the technology has been price: Ahmadian says MR-based dampers are several times more expensive than conventional hydraulic units. But the fluid’s price has fallen as much as 30% over the past decade, and the professor foresees a time when the price difference is only two times greater.
“If it’s twice as expensive (as hydraulic dampers) and I’m getting four times the benefits, then it becomes a no-brainer to use an MR damper,” he tells WardsAuto.
The fluid contains iron particles that can be magnetically manipulated nearly instantaneously to form a rock-hard suspension or create a soft, billowy feel, depending on dynamic input. Many luxury vehicles using the technology allow drivers to switch between two or three suspension settings, generally including “comfort” and “sport.”
Ahmadian says there is no better approach to isolate vibration than MR fluid.
MR dampers, for instance, require no moving internal parts, while conventional shock absorbers need shim valves or other valving to govern the flow of hydraulic fluid.
An MR-based damper uses a piston that incorporates one or more electrical coils. Current is applied to the electrical coils to generate a magnetic field. Its rheology, or ability to flow, is altered when that fluid is energized.
“That rheology changes directly proportional to how strong that magnetic field is,” Ahmadian explains. “The strength of that field is directly proportional to how much current is passing through the coils.”
The result is a suspension that reacts to every situation and keeps the vehicle firmly planted.
“It gives us the ability to control the body in vertical directions as well as in pitch (and) roll,” says Ahmadian, who worked for Lord several years ago. “That’s the part that’s really attractive. We’ve done studies showing it also enables us to prevent the body from getting to its rollover threshold.”
After 10 years in the market, he says MR-based dampers are as durable as conventional shock absorbers.
Delphi integrated Lord’s MR fluid in its MagneRide technology – used across the Cadillac portfolio and by Ferrari – before exiting the suspension business as part of bankruptcy-fueled restructuring in 2005.
Delphi completed the sale of its brake and suspension business to China-based BeijingWest Industries in 2009. Today, BWI remains the primary marketer of MR-based suspensions, Ahmadian says.
However, he notes BASF has invested heavily in attempting to join the market, but he has not had an opportunity to evaluate its product.
“I know there are suppliers in China and India that have attempted to develop their own fluid or (already) have their own fluid,” Ahmadian says. “As to the quality of the fluid, how stable it is and how well it works, I have no idea.”
Any company attempting to enter the MR market will need to navigate through more than 110 patents worldwide held by Lord for controller algorithms, the fluid and its applications.
Besides suspensions, Lord sells an aftermarket damper named Motion Master for the underside of seats used in heavy-duty trucks. The retrofit system displaces the conventional hydraulic damper normally installed under the seat to control the seat’s motion and transmitted vibration.
“A truck driver spends extended hours on that seat,” Ahmadian says. “Over the long haul, it really makes a huge difference to them. The ones who ride on Motion Master seats swear by it.”
Light-duty pickups currently do not use MR-based suspensions, but the professor says it’s only a matter of time before it happens. Old-style leaf springs in the rear could work together with MR dampers at all four corners to improve the ride and handling of a pickup.
“If I have a pickup, there’s even more benefits with MR,” Ahmadian says. “It allows us to better adjust the suspension to that load variation.”
