Since Mercedes-Benz offered the first car sunroof in 1932, Matthew Beecham finds that the ways in which automakers have sought to let the sun shine into the cabin have become increasingly complex.

Top trends

Panoramic sunroofs stretching the length and breadth of a vehicle are becoming increasingly popular on both sides of the Atlantic. These designs give the best of both worlds: saving on cost (compared to a convertible) and adding to the versatility of the car.

“We still see a strong consumer need for light and air,” said Jos Sanders, director of advanced technology at Inalfa Roof Systems Group.  “The consumer understanding of sunroofs has matured and we see a growing population of consumers willing to pay for light and air. This is reinforced also by a growing group of second-buy consumers.”

In terms of future trends, Thomas Becher, chief engineer of ArvinMeritor’s roof systems business based in Dietzenbach, Germany, sees a trend towards roof modules with integrated opening systems (i.e. multi panel) because the modular technology supports the trend towards top loading assembly processes on the car manufacturer’s assembly line.  Becher believes that this provides potential for utilisation of various roof options on one body interface.

Sanders also sees a trend in growing size of sunroofs with bigger take-rates and across more vehicle segments. He told us:  “This simultaneously drives a sense of urgency for lowering the total weight of sunroofs. Customers and consumers do appreciate that low-weight solutions require more advanced material choices and technologies. However, there has to be a clear performance factor to rectify additional costs. This is where technologies like solar-powered sunroofs are struggling. The output performance and cost structure are not balanced yet.”

The desire of many car designers to include increasingly large amounts of glass in their cars presents glassmakers with new challenges because glass cannot be shaped at will like steel or plastic.  Other trends include producing a smooth roof line using several glass panels, e.g. producing windscreens which extend up into the glass roof.

Yet is there still a move toward a bottom-load, big roof? i.e. a middle niche developing which is between a traditional sunroof and an all-glass moving system.  “We see this as a trend,” says Sanders, “which means the market for these roofs is growing. But we don’t see this as a fashion trend but as a strongly fact driven trend based on volumes, specific markets and vehicle segments and styling.”

Becher agrees that the bottom-load and the top load systems exist in parallel today. He told us: “Due to particular applications such as some SUVs we will still see bottom load large opening sunroofs in the future.”

SUVs represent the largest growth opportunities for the wide opening panorama roofs, followed by sedans.  “By bringing the previously SUV dominated roofs down to crossover you also see a trend in more carry-over content,” said Sanders.  “This finally will make these roofs available to more vehicle segments. This is in line with normal implementation paths for new vehicle technology.”

Becher added:  “There is a trend to implement the same type of sunroof concepts that have initially been developed for the SUVs on to other larger roof structures like middle class sedans and station wagons as carry over.”

In terms of the further development of sunroof design, Becher concluded:  “Sunroofs are becoming an increasingly important styling element in passenger cars. Also the future development will have to cope with the platform approach of the OEMs, i.e. provide modular solutions that can cover a whole range of vehicles with one basic concept. On a component level we will see light weight solutions, new shading systems, solar panels and switchable transparency.”

Simplify

Are roof systems becoming so complex that the next challenge is to simplify them? Becher points out that future sunroof development is under the same cost pressure as the rest of the industry. He told us:  “Our solution is to develop modular concepts on the subsystem level, i.e. a design that provides solutions for various demands within one basic concept. Demands like various shading systems, solid and transparent panels, integration of solar options etc. The time for sophisticated and costly developments for niche products is over. Modularity on all levels seems to be the answer.”

Sanders agreed that the challenge is to simplify. He told us:  “We do believe that there is a market for highly innovative roofs which will be targeted at vehicles bought by early adapters. The commodity sunroof will borrow the technology from these innovative roofs at some point in the future.”

Joerg Palmersheim, head of BaySystems Automotive, Diversified Industries and Thermoplastic Polyurethanes EEMEA, believes that there is still room to include more technologies and functionalities in a roof module, for example antenna systems and solar panels or the use of solar active foils on roof modules. “The key for success,” says Palmersheim, “lies in intelligent processing technologies that offer simplification in assembly and disassembly.  Increasing modularity allows more design flexibility.  It’s not a matter of how many functionalities you include but how you include them.” BaySystems Automotive is a business unit of Bayer Materialscience

Jan Just, executive vice president of Magna Car Top Systems, reckons that today’s cost- and mass-reduction requirements drive simpler solutions with lesser components. “Advanced design and analytical aids as well as early collaboration as outlined previously are enabling teams to achieve these goals.”

Retractable roofs

Meanwhile, the expanding convertible segment is crossing all vehicle segments.  It is no longer a preserve of the luxury class.  Roof makers say that growing consumer acceptance as well as all-weather convertible top concepts such as its retractable hard-tops (RHTs) will contribute to the market’s expansion.   While electrically operated convertible-roof systems are industry standard for luxury vehicles, roof makers are continuously working toward developing smaller, lighter and cheaper systems.

In terms of the pace of growth of the RHT market in North America, Just told us: “Before the economic downturn we have been seeing a slow but steady growth of the RHT market in North America. With the recent discontinuation of vehicle lines/brands (Cadillac XLR, Pontiac G6) the North American market appears to have declined.  As the carmakers are currently redefining themselves, future growth is expected. OEMs will keep using convertible technologies to distinguish themselves and draw customers into showrooms. The actual rate of growth for the overall North American convertible industry will depend on the recovery of both, the local automotive industry as well as the economy.”

Over the past few years, we’ve seen the emergence of two, three and four-part retractable hardtops.  Just noted that multiple-panel retractable hardtops traditionally require more complex system architecture and therefore add mass and increased structural requirements to the vehicle. “Alternative materials, simpler solutions, and increasing production volumes may yield more competitiveness compared to fixed-roof vehicles in the future.”

Yet getting the balance right between weight, packaging, styling, material, price, crash requirements, luggage compartment space and stiffness is becoming even more important.  And the more sections the RHT folds into, the greater the complexity and cost. “Early involvement with the vehicle manufacturers,” concluded Just, “enables proactive influence with styling and vehicle architecture versus reactive development, which typically drives complexity and cost.”

Matthew Beecham

‘Beechy’