Look out BMW, that could be a Volvo coming up in the rearview mirror. By integrating automotive electronic control of suspension, braking, traction, and stability, the Swedes' S60R performance sedan (300 hp, 295 lb-ft torque) aims to provide a good handling, safe car to suit any driving style. And that ranges from the soccer mom who wants a bit of driving fun, to the performance driver who'll be on the track some weekend.
What Volvo calls its Four-C (Continuously Controlled Chassis Concept) technology is key to making this car handle well over a range of road surfaces, and thus contribute to accident avoidance safety. Accelerometers measuring longitudinal, lateral, and vertical accelerations, along with sensors for wheel rotation and vertical movement, steering wheel position and velocity, yaw rate, engine torque, and ABS brake and stability system outputs, feed data to a central control unit (see figure).
Five hundred times a second, this controller calculates new settings for the small electromechanical valves in each shock absorber to change the damping rate, and thus the stiffness of the shocks. The valves are two stage, soft-opening devices that only move 0.3 mm from full open to closed. Damping force is changed in from 5-15 msec, depending on the size of the change.
Öhlins Racing AB (www.ohlins.com/ces.shtml) developed the shock technology initially for professional racing motorcycles. According to Lars Erik Lundin, VP and general manager of Volvo's Camarillo, CA-based Monitoring & Concept Center, cost of these specialized shocks was prohibitive for a production car. But by joining with U.S. shock maker Monroe, the Öhlins system could be manufactured in production quantities for allowable costs.
Three in one: Driver steering, brake, and
throttle inputs, plus chassis sensor readings, dictate the degree of
individual shock damping. Three chassis control mode settings change
parameters in, and application of, the various algorithms that feed
continuous microvalve inputs to the shocks. This tailors the blend of
characteristics, sucha as ride comfort, driving control and active safety,
to driver preference.
While the Four-C system is reactive, its computational speed allows it to foresee how the forces and driver inputs acting on the car will cause the vehicle to react and to prepare for them. For instance, in a hard stop, the controller obtains brake pedal data several milliseconds before the brake pads touch the disc. The system will increase damping on the front shocks, stiffening them to offset "diving" of the nose of the car, increasing control.
Likewise, on acceleration, rear shock damping is increased to mitigate the front of the car from lifting. A quick turn of the steering wheel produces a controller output before the car actually changes direction, stiffing the front outside shock, softening the inside rear one, and applying more torque on the rear wheels—all of which lead to improve turn handling.
A la mode
A driver can select from three Four-C control modes—Comfort, Sport, or Advanced. Suspension Dynamics Engineer Marcus Rothoff notes that the mode settings change parameters in, and application of, the various algorithms that continuously feed commands to the shock valves (see diagram). Each mode tailors the blend of characteristics, such as ride comfort, driving control, and active safety, for driver preference on a given road. "Compared to standard shocks, the sum of these properties is improved in all settings, but of course with different 'blends'," he adds.
Shocking: Comfort concerns on rough
pavement (left) require programming S60R shocks for more shock piston
movement to prevent a jolting ride. Driving on a smooth track (right)
allows dialing in stiffness to keep the tires "planted" for maximum
The Comfort setting allows the wheels to follow best any bumps in the road. The shocks soften car body movement, "floating" it more so it doesn't experience every undulation. In Sport mode, the shocks are set stiffer, reducing roll during hard cornering. The Advanced setting maximizes the grip of the tires on the road without regard to ride comfort—and throttle response is also quickened.
But beyond the electronic legerdemain, the suspension is also designed with inherent passive features that improve handling. The multi-link rear suspension, which permits independent rear wheel movement, incorporates a small amount of "steering effect." During a turn, this allows the rear wheels to steer slightly in the same direction as the front wheels for what Volvo terms "stable steering responses."
While handling and electronic integration are key features of the S60R, other systems contribute to the car's performance. The R version uses the same Haldex electronic-controlled coupler to transfer power to the rear wheels, similar to previous all-wheel drive Volvos (see DN 12.03.2001, p. 25). But in the R it is programmed to transfer power more rapidly to the rear wheels (and keep it there longer) from the normal 95-to-5% front-to-rear distribution in order to provide more oversteer to aid in turning.
Aerodynamically, a small spoiler on the bottom of the car about 6 inches behind the front fascia and a diminutive lip on the rear trunk lid cut lift forces on each end by 25 and 20%, respectively—helping to keep the car wheels planted to the pavement. To improve airflow over and through the engine compartment, the grill opening is smaller and lower down than a standard S60. A larger inlet at the bottom of the front bumper feeds cooling air to the radiator and twin intercoolers for the turbocharged engine inlet air.
Weighing in at 3,571 lbs, the 300-hp S60R has a sports car-like weight-to-horsepower ratio of 11:9, which contributes to a zero-to-60 time of 5.4 sec. Thus most important for a car capable of such speed is the ability to stop quickly.
To do this, Volvo engineers use 13-inch diameter Brembo disc brakes with four-piston aluminum calipers. Four pistons instead of two keep the pads parallel to the discs under high heat loads, and the aluminum also helps with heat dissipation.
Finally, while performance vehicles, the S60R and V70R preliminary EPA mileage numbers are 18 mpg city, 25 highway, and 21 combined. List price for the car is $36,835 and $38,325 for the wagon.