Continental develops intelligent car windows

Automotive supplier Continental is to showcase a demo vehicle in which all windows can be darkened at the touch of a button at the Consumer Electronics Show (CES) in Las Vegas from January 6–9, 2016. ‘Intelligent Glass Control’ uses special films which are inserted into the glass and which change their transparency through electric control signals.

“The selective, incremental darkening of the side and rear windows, as well as parts of the windshield, not only offers considerably increased comfort for passengers, but also makes driving safer,” explains Andreas Wolf, head of Continental’s Body & Security business unit. A typical example is a low sun on the horizon. The driver's hand instinctively goes from the steering wheel to the sun visor. Wolf says, “This results in both impaired visibility and a brief decrease in control of the vehicle." In the future such situations can be detected in advance, and the windows could darken automatically before the event even occurs.

Darkening saves energy

By using these films, the solar radiation can be reduced more effectively than with other technologies. “This means that we can keep the heat out of the vehicle and significantly reduce the interior temperature," explains Wolf. This relieves the air-conditioning unit, which can then be smaller, more energy efficient, and therefore much lighter in weight. Furthermore, the added weight of the sun visors and mechanical blinds is removed, with positive effects on the environment. “Our calculations have shown that the CO₂ emissions are reduced by a good four grams per kilometre thanks to these measures, thus increasing the range of electric vehicles by around 5.5%."

In addition to the reduced heat in the interior, the darkening also effectively enhances privacy. “If the vehicle is parked, the windows darken automatically, so the inside of the vehicle cannot be seen from the outside." Intelligent Glass Control also gives designers new options. According to Wolf, the glass surfaces could be extended further, without having to cover certain areas mechanically. The available film still has a slightly blue shimmer, but in the future Continental is expecting a broader range of colours, opening up additional design possibilities. Other effects, from coupling light effects through energy recovery to touch screen functionalities, may also be possible.

Particles align under current

Films in which embedded particles can be aligned when a voltage is applied, and which can be used for targeted darkening of the window, have been available for a long time already. Up to now, however, this technology has only been feasible in the roof area for a small number of high-end cars. Engineers at Continental are demonstrating the intelligent activation of the ‘Suspended Particle Device’ film technology also for side and rear windows and the windshield for the first time in a test vehicle. Due to legal requirements, however, it is initially only shown here in the permitted area of the sun visors.

This production-ready film technology is based on embedded particles, which arrange themselves randomly when unpowered and darken the window from outside, while retaining transparency from the inside to the outside. If a voltage is applied, the particles systematically align themselves in parallel, so that the window becomes permeable to light in both directions. The connection to the vehicle system enables the windows to lighten automatically when you approach the vehicle with a key or smartphone," says Wolf.

This film is still rather cost-intensive for mid-range vehicles with large glazed areas. However, due to further promising developments with initial applications in the mobile area, it is anticipated that the prices will quickly drop. Other alternatives to film technology are based for instance on liquid crystal polymers or electrochromism. The latter uses the ability of molecules and crystals to change their optical properties under the influence of an electric field or a current flow. This technology is already deployed in the car in order to darken the interior and exterior mirror and thus prevent glare effects. The disadvantage of larger surfaces is the high energy requirement needed to achieve short switching times.

Control is what counts most

Which technology finally prevails is not crucial, as they all need to be controlled electronically. The essential know-how is in the software and the intelligent connection to the vehicle system. Andreas Wolf: “Today it is just a question of when intelligent glass is coming. At Continental we use our know-how for the entire system and can therefore integrate the desired functions into our electronic control units. Here we adjust the algorithms so that the behavior of the windows offers maximum safety and comfort for the driver while improving emission values. The appearance of all windows is optimized with an intelligent reaction to the changing lighting situations as well as automatic compensation of temperature and aging effects."