A smooth ride and sharp handling meet in the latest suspension technology
An important goal of Ford Motor Company's work in suspension technology has been to improve the shock ratio, a measurement that compares the wheel motion to the damper motion, explains Ali Jammoul, Ford's chief chassis engineer. Dampening is the process of controlling vibration and unwanted motion that results from the movement of the suspension in response to the road.
The ideal shock ratio is a one, a goal Ford has achieved on Taurus models, Jammoul says. "The closer you get to one, you really do improve the isolation, quietness and damping of the suspension." Isolation refers to a vehicle's ability to isolate road shock from the passenger compartment.
Ford also has been "quite persistent in reducing the weight of the suspension," Jammoul says. "With a reduction in weight comes many good things. The unsprung mass is lower, which helps dynamics and handling and helps with fuel economy." A vehicle's unsprung mass is essentially the mass between the road and the suspension.
In an era when owners are keeping their cars longer than ever, equipment longevity is more important than ever. With that in mind, Jammoul says, "We have improved our attachments such that all bolts and fasteners have green coatings that improve serviceability at high mileage; they're easier to disassemble for service." The enhanced finishing helps avoid corrosion, which can make parts difficult to remove.
Electronically controlled shocks are another key development area, notes Jammoul. That approach, also known as an active system, uses sensors to dynamically adjust shock absorbers in response to road conditions. "Electronically controlled shocks can improve ride without sacrificing steering or good controlled handling," Jammoul says. "Electronic systems should appear on some luxury vehicles."
Several manufacturers already have introduced electronic controls for their suspension systems, at least on certain models. The Acura MDX has had an active damper system since 2007 that uses electronically controlled magneto-rheological fluid. Viscosity of the fluid is controlled through a coil that generates an electromagnetic field when current is passed through it, enabling precise adjustment of the damping force in as little as five milliseconds, the manufacturer says. Drivers can adjust the system to operate in either a "sport" or "comfort" model. Sport mode prioritizes handling response, vehicle body control and tire adhesion while comfort mode prioritizes road isolation.
"The system has been very well received," an Acura spokeswoman says. "The car handles very well under sporty conditions and you can definitely feel the difference when you put it on the comfort setting. It's a very quiet ride."
General Motors recently introduced the second generation of its electronically controlled magneto-rheological suspension system on the Corvette and Cadillac CTS-V. Another new development at that company is a high performance strut front suspension, which will be included on a new vehicle that will be launched this summer. "The HiPer Strut steering geometry reduces steering wheel shake and improves on-center feel," comments Scott Kolp, lead engineer for suspension systems at General Motors. "It also virtually eliminates torque steer behavior found on other front-wheel drive vehicles."
A vehicle's geometry also impacts the choice of its front suspension. "In a transverse engine front-wheel-drive car, space is at a premium to fit the engine sideways, so McPherson strut suspensions are common to maximize engine compartment room," notes Chrysler's Erich Heuschele.
A front-wheel drive minivan also would typically use a strut front suspension, along with a twist axle rear suspension, he says. "A twist axle suspensions's big benefit is in the packaging. The whole suspension is below the floor of the vehicle," explains Heuschele. "The PT Cruiser would not have anywhere near the interior space if it did not have a twist axle rear suspension."