Controlled incremental darkening of car windows prevents heat entry and lowers CO2 emissions.

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. 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 the 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. Connection to the vehicle system enables the windows to lighten automatically when a driver approaches the vehicle with a key or smartphone.

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, Continental anticipates that the prices will quickly drop. Other alternatives to film technology are based 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.

Which technology finally prevails is not crucial, Continental says, as they all need to be controlled electronically. The essential know-how is in the software and the intelligent connection to the vehicle system.

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.

—Andreas Wolf, head of Continental’s Body & Security business unit

By using these films, the solar radiation can be reduced more effectively than with other technologies, keeping heat out of the vehicle and significantly reducing the interior temperature. This in turn 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.

Continental’s calculations have shown that the CO₂ emissions are reduced by a good four grams per kilometer due 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. The available film still has a slightly blue shimmer, but in the future Continental is expecting a broader range of colors, opening up additional design possibilities. Other effects, from coupling light effects through energy recovery to touchscreen functionalities, may also be possible.