Alert motorcyclists have an ability to gauge the likely friction levels of a road surface well in advance of their progress; they need to, because they are acutely aware of the possible consequences of slippery roads. Drivers of cars and larger vehicles, though, do not generally have quite the same detailed, forward-looking visual acuity and environment analysis.
A significant friction cue is the light reflected from a road surface. Sometimes this can be a subtle variation that a driver, isolated from the exterior environment and sitting well back behind a windshield, may not immediately assimilate.
Now, Continental is developing integrated sensor technology—including a polarization camera—that can help “recognize” road-surface rain, snow, and ice, and act as an early warning system to alert drivers on final approach to a potentially hazardous area.
The company’s work is centered on the Friction Project, part of the European Commission’s (EC) 6th Framework Program. The EC part-funds the project, which also involves other companies.
Active safety systems such as ESC (Electronic Stability Control) and ABS have become the norm for products in many markets and will very effectively alleviate the negative effects on vehicles on low-friction surfaces, helping to control a vehicle that loses—or may incipiently lose—adhesion through corners or under braking. With the technology now under development, Continental is trying to look ahead of a vehicle well before there is even a hint of drama and give the driver a warning of reduced friction.
Described as a “sensor fusion” system, it takes data from a vehicle’s dynamics sensors and interprets it together with information from environment and tire sensors.
“The basic idea is to inform the driver as soon as he or she gets too close to the limits of friction between tire and road,” explained Continental in a statement. For that purpose, the system estimates the required friction used for a particular driving maneuver, estimates the maximum available friction (friction potential), and calculates the difference.
The big challenge was to integrate both vehicle and environment sensors signals and to create a reliable decision-making sub-module.
Strategies used to estimate the friction by calculating the vehicle’s dynamic response include the computation of longitudinal and lateral acceleration, wheel speeds, yaw rates, and steering wheel angle.
Based on a lateral-dynamics model that describes how the vehicle should react under ideal ambient conditions, the actual vehicle reaction indicates the real-time level of friction. However, Continental decided more information was needed and collected it via friction estimation based on steering torque, a system developed by Centro Ricerche Fiat.
Once the sensor fusion has calculated the emerging situation, information on the road conditions can be transmitted to the driver via a HUD (head-up display), by an audible warning, or possibly a haptic alert—or a combination of all three.
There are five environment sensors providing data to the second sub-module that computes the overall environment conditions.
A polarization camera detects differences in vertical and horizontal polarization caused by road surface conditions at least 5 m (16 ft) and up to 20 m (66 ft) ahead of the vehicle. An optical sensor is crucial to measure light levels reflected by the road surface between 0.4 and 1.5 m (1.3 and 4.9 ft) ahead of the front wheels. In parallel with these sensors, a laser scanner monitors ambient weather conditions for cues that may include snowflakes and rain drops 50 to 100 m (164 to 328 ft) ahead of the vehicle.
Ambient temperature and road surface temperatures are also monitored.
Tires have intelligent sensors checking distortion of the rolling carcass to detect the onset of aquaplaning.
The sensor fusion system takes all this information and checks it against thermometer readings to assess credibility and the likelihood of deteriorating road conditions—and subsequent likely reduction in surface friction.