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Sedan grips Canadian ice with every wheel
by Benjamin B. Ames, Senior Editor -- Design News, March 11, 2002
Calgary, Alberta — Volvo's new S60 AWD sedan swaps power between slipping tires to guarantee a smooth trajectory through slick turns.
In a recent test drive, I did my best to spin or skid the car, and failed everywhere but pure ice. The drive covered hundreds of kilometers of roads through the Canadian Rockies surrounding Nakiska and Canmore, sites of the 1988 Winter Olympics.
We didn't see much pavement all day; just snow and loose gravel. Cinder-strewn hairpin switchbacks with fallaway curves led to one-way bridges over half-frozen brooks. Eyes on the road? Not easy—driving distractions included big horn sheep licking road salt along the shoulder.
Yet time after time, this startled driver cancelled his rookie impulse to over-steer or to brake too late. There was no need—the car had already slowed, damping the dangerous spin of skidding tires, or adding a touch of brake only to the gripping wheels.
How does the S60 do it? It's not a Vulcan mind-meld, it's a trio of systems—AWD, TRACS, and DSTC—communicating through the car's multiplex computer system.
On a smooth, dry road, the car is basically a front-wheel drive. But when the all-wheel drive (AWD) detects a difference in the rotational speed of front and rear wheels, it opens a control valve in proportion to the amount of slip. That allows pressurized oil to reach the wet clutch plates in the rear differential, transferring power to the rear wheels. Created by Haldex (Stockholm, Sweden), the system uses an electric pump to maintain oil pressure, for quick deployment (see DN 12.3.01, p.25). To calculate how much power to share, it also monitors throttle position and communicates with the TRACS traction control system.
Finally, the DSTC (dynamic stability and traction control) is an option that was first introduced in the Volvo S80. Unlike the AWD, it knows the difference between right and left, so it can add shades of brake or dab a touch of throttle to any wheel.
It adds up to the kind of correction you don't really notice until it's taken away. Of course this car accelerates hard from zero to 60 on uphill, snowpacked roads—don't all cars? Well, no. An amber-colored dashboard light flickers when the DSTC kicks in. But it doesn't engage until you need it, like a child learning to ice skate between his father's knees.
Perhaps the easiest way to notice the system was on an orange-coned obstacle course. With a stopwatch ticking, we gunned the sedans through slalom curves, first with the DSTC on, and then without. The resulting spins and donuts presented just one question—why would any winter driver turn this thing off?
The answer—this car will brake faster without DSTC under arcane conditions, such as driving with studded tires on a snow-covered frozen lake, where an initial skid is required for the cleats to grip, says Lars Erik Lundin, VP and GM of Volvo's monitoring and concept center (Camarillo, CA). He predicted the off-switch would be phased out in future models.
Volvo has positioned the car against the Mercedes-Benz C-Class, Lexus IS, BMW 3-Series, Acura TL, and Audi A4 (the strong market leader in AWD sedans). The company also claims buyers from the ranks of former Honda Accord, Toyota Camry, and VW Passat drivers.
The car I drove cost $37,200 fully loaded (including snow tires), up from a base price of $33,375. Itemized, it's $1,750 extra for the DSTC option, and another $450 for the winter package (although this is free in some promotions). The standard powertrain is a 2.4-liter, 5-cylinder aluminum engine with light-pressure turbocharging.
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