The serious Swedish engineer started the XC90 and stepped on the accelerator. He ran it at 35, 40 and even 50 mph, powering through the slalom with complete control. It was fun, and enlightening, to watch how the vehicle stuck to the road incredibly well, without a nanosecond of instability, even after the Pirelli Scorpions became overheated.
The main reason for this show of stability, Noren explained, has to do with the vehicle's overall dimensions. Although the XC90 T6 has a ground clearance of 9.2 in., its center of gravity is only 26.14 in. high, only 3.5 in. more than the XC70's cg. And the wide tracks (64.3 in. front, 63.9 in. rear) give a stability factor of 1.22, "a very good figure for an SUV," said Noren.
The innovative Roll Stability Control can be seen as the eyes and ears of the DSTC and was designed to minimize the risk of rollover due to abrupt directional changes. RSC is in operation from 6 mph up to top speed in all situations-cornering, evasive actions, acceleration and braking. Using gyroscopic sensors to measure roll angle (the only system now on the market to do this) and roll rate, it informs DSTC, which in turn intercedes to reduce lateral forces and the risk of rollover.
DSTC itself collects data from a steering wheel angle sensor, lateral force sensor, yaw rate sensor and speed sensors, and then by comparing the information calculates if the car is moving in the intended direction or not. DSTC interacts by braking one or more wheels and/or reducing engine torque to keep the car on track by transforming the impending oversteer into understeer.
Many of these developments came out of crash tests. Richard Nilsson, safety attribute manager, said he and his team crashed at least 40 XC90s, using them over again to simulate other crashes. The XC90's safety systems include Volvo's IC or Inflatable Curtain, which runs the length of the passenger compartment, offering protection for all three rows of seats, the only vehicle to do so. Also, it inflates for up to 6 sec. to help keep occupants in the vehicle as well as protect them during side impacts.
Richard Nilsson explained, "We use a method called FEM (fine element method) to simulate crashes in the computer. All parts of the vehicle (body, chassis, engine, etc.) are divided into small elements. The size of the elements varies from 10x10mm to 20x20mm, and the whole car consists of approximately 450,000 elements. A typical analysis of a 'computer crash' would start with looking at the behavior of the entire car on the screen. Then we start to study how each component deforms or moves.
"A big advantage compared with real crash tests is the possibility to 'uncover' any component and study its behavior. Then, when the visual observation is done, we look into forces, displacements and other physical parameters. When the analysis is finished, we decide on how to redesign components that are not working as intended. Possibly this could be done during a normal working day, and a new crash simulation could be started before we leave the office. A crash simulation takes about 15 hours in the computer, so the new results would be ready the next morning."