Issue: Dec 2013


Lightweight windshields going mainstream



by Nick Palmen


Stone impact resistance of windshields comprising different combinations of inner and outer glass thickness. Higher values indicate better stone impact resistance. Here a 1.8/1.4 windshield has a better resistance than a standard 2.1/2.1, even though it is 1mm thinner.
Lightweight windscreen technology developed for premium marques such as Ferrari is now moving to production cars.

Automotive Industries (AI) asked Patrick Dupin, chief executive officer of Saint-Gobain Sekurit what the brief was for the windshield for the new LaFerrari.

Dupin: On the previous model, the cutting-edge technology for automotive glazing was the low-emissivity roof on the Ferrari FF, the so-called SGS ComfortSky. By providing an impressive vision without disturbing heat radiation in summer and prevention from the cold wall effect in winter, it set the standards for the objectives for the new model.

The technology allowed for savings on space and weight through the removal of the roof sun shade shutter. One of Ferrari’s major objectives for the new model was weight reduction. The LaFerrari, the latest sports car from Maranello is the first car with a lightweight innovation in a 4mm windshield. Saint-Gobain Sekurit’s latest technology enabled the luxury car manufacturer to save 1.3kg on the windscreen alone.

Compared to current standard thickness of 4.5mm, the introduction of this lightweight 4mm innovation reduces the glazing weight by 12%. The thicknesses of each layer of the glass sandwich with the 0.76mm PVB interlayer has been reduced to 1.8mm for the outer pane, and 1.4mm for the inner pane.

AI: How is Sekurit’s latest technology enabling the car manufacturer to save weight?

Dupin: When every gram counts, lighter windshields contribute to keeping the weight down. Since its introduction in 1981, the thickness of the laminated windshield has been constantly reduced. Today windshields are usually 5mm or 4.5mm thick. A 5mm windshield is made up of an outer pane and inner pane of 2.1mm each with a 0.76 PVB interlayer. The adaptation of the glass thicknesses of 5mm into 4.5mm yields already 1.5kg of weight reduction for a windshield of 1.2m2. With the use of the new innovative 4mm windshields another 1.5kg can be saved compared to 4.5mm, and 3kg can be saved compared to 5mm.

AI: How did you reduce weight without compromising safety, robustness and comfort?

Dupin: A major function of the windshield is its contribution to car safety, which is defined by various requirements in ECE R43 and similar standards. Thanks to the chosen product, and process parameters for glass and interlayer, light-weight glazing shows in such tests comparable results to standard glazing to assure the safety of the passengers. In some cases like EuroNCAP pedestrian impact they are even superior. Robustness of the glazing is another important aspect. The stone-impact-resistance of windshields is of common interest as the replacement of the windshield is costly and annoying.

Hence, car makers and end consumers have the aim to assure or even improve the stone-impact-resistance of windshields. The outer and inner panes of more common 5mm windshields are of the same thickness, whereas the new 4mm windshield features an asymmetric combination. A 4mm windshield is configured with a 1.8mm outer pane and a 1.4mm inner pane with a 0.76mm PVB interlayer. Thus, the inner pane is notably thinner than the outer pane. Through asymmetric design, the lighter 4mm windshield shows an increased stone-impact-resistance compared to 5mm thick windshields.

Acoustic properties must also be considered when it comes to good overall comfort in lightweight design. A large amount of exterior noise can enter through the windshield of the car. Hence it is important to pay special attention to this property, and indeed it has been possible to develop thin windshields with a special “acoustic” interlayer that lets less noise into the car than standard windshields. This means that solutions have been found to beat the classical mass effect and to provide at the same time low weight and good acoustics.

AI: Is there an opportunity for other car manufacturers to experiment with the new technological solutions?

Dupin: We can say that several car manufacturers are much more advanced than experimenting, which means that we will see low weight glazing on new car models from different brands in the coming years. Besides the indicated weight reduction through windshields, there are further weight reductions possible through lightweight glazing in the other body openings. In total, for a family car with about 5.5m2 glass surfaces, the maximum possible weight saving through glazing is estimated to be around 10 kg.This results in a fuel saving of 0.037l/100km being equivalent to 0.847 g CO2/km, when taking the fuel reduction value FRV into account. With an average annual mileage of 24,000 km per year, one obtains approximately 20 kg less CO2 emissions per car every year.

AI: Would the new lightweight technologies for windscreens be limited only to the premium sports automotive segment?

Dupin: Consequent development of lightweight design plays a major role for further fuel consumption reduction in all segments. Hence low weight windshields will find applications in all car segments. As an example, the new Citroen C4 Picasso will be equipped with this innovation. Due to the large size of the panoramic windshield of the C4, the weight saving in this car is as much as 2.6 kg.

AI: Can we expect any further models with the new lightweight windshield to follow soon?

Dupin: This new lightweight technology will be featured in two more car models in 2013. And in 2014 several further car makers will start to use this technology. Over the next five years we expect a very rapid growth of this market, since many car manufacturers are seriously considering applying the technology to future models.

AI: What else can we expect from Sekurit in the near future?

Dupin: With our future solutions we support general trends in automotive glazing. The ability to offer environmentally friendly solutions such as solar control glazing for reduced AC energy consumption will be key. Another focus is the contribution to the vehicle design: automotive glazing is becoming bigger like the C4 Picasso, and more complex as in the Peugeot RCZ. Finally, end consumer expectations regarding comfort and perceived quality are becoming higher and higher. Therefore, heatable and heat-reflecting windshields such as the SGS ClimaCoat all-weather windshield are important innovations for all car makers.

AI: And for the long term, what are you focusing on?

Dupin: General principles for branding and development in the automotive industry are freedom, status, ownership, environmental awareness, and driving pleasure. For the long term, our further development focuses includes designing sophisticated products for these future mobile living spaces. Following fundamental trends by offering corresponding innovations is the key for long-term success.

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