Hic Volvo Non Volvet, meaning this Volvo
won't roll over in Latin, is evidenced by this moose test. (Volvo is I
roll in Latin) Avoidance maneuvers demonstrate the XC90 electronically
minimizes any tendency to rollover.
Newton, MAWhile the name Volvo means "I roll" in Latin, the company's new XC90 SUV has an electronic system that helps keep it from "volvet" (rolling over). The rollover tendencies of high-center-of-gravity SUVs are not only the concern of many of their drivers, but both private and government safety organizations as well. But now, thanks to Ford, brake system and electronics supplier Continental Teves (www.contiteves.de), and Volvo engineers' processing and sensor developments, SUV drivers can feel safer about everyday driving and emergency maneuvers. And because the rollover system was developed in conjunction with Ford's Advanced Vehicle Control Team based in Dearborn, MI, it will not be a far stretch to see the technology on the company's U.S.-developed SUVs soon.
Basically the engineers built upon already existing dynamic stability and traction control (DSTC) systems, that reduce skids and wheel slipping tendencies, respectively, which in turn use ABS (antilock braking system) sensors at each wheel. They also added RSC (roll stability control) software to the DSTC control unit and a Continental Teves roll rate sensor. This sensor, located under the front passenger seat, consists of a micromachined silicon tuning-fork gyro aligned with the roll axis similar to the yaw rate sensor that detects skidding about the vertical axis (see figure). System architecture is a high-speed CANbus. If algorithms detect an impending rollover, say to the left, commands may be given to cut the throttle (reducing centripetal acceleration) and to apply the brakes on the left side wheels (differentially front and rear, hinging on load distribution) to impart yaw and roll to restore an upright attitude.
But with any electronic-based control system, there is always the question of how to account for a spurious signal that may cause an incorrect response. "The biggest challenge of designing a safety critical system is to make it safe in all driving scenarios and environments, without unnecessary intervention," says Volvo Active Safety Design Engineer Hans Jonsson. "Sensor monitoring algorithms ensure that the signals are correct. In the case of unrealistic signals, these are 'captured' by plausibility algorithms containing vehicle models, state estimators, etc., preventing false activations," he notes. "Wheel lift" algorithms also monitor the state of each wheel in addition to rollover inputs.
The control algorithms are fairly complex, but fairly straightforward, adds Phil Headley, chief engineer for Advanced Technologies at Continental Teves. "Developing them involves understanding the reaction of a vehicle in an impending roll situation plus accounting for the rates, angles, and conditions (such as steering and braking) leading up to that point," he notes. To steady-state monitor the sensors, Headley adds, "Failure recognition in the software sees if a sensor [by the nature of its output] is not functioning correctly and also monitors output by calculating other sensors' rates."
Inherent safety, too
Besides the RSC system, the XC90 has other design features to improve rollover safety. Engineers kept the center of gravity low by having a separate interior floor and structural frame. If the SUV does roll, high strength boron steel in the roof structure helps keep the roof from collapsing. And a front cross member is positioned to interact at the correct bumper height of any vehicle that may be impacted in an accident, triggering its safety systems. For a ride-and-drive review of the XC90, visit designnews.com.