Since Mercedes-Benz offered the first car sunroof in 1932, the ways in which automakers have sought to let the sun shine into the cabin have become increasingly complex. More recently, we’ve seen the emergence of two, three and four-part retractable hard-tops (RHT). With a little help from Webasto, VW has pushed back the boundaries by offering a five-part RHT. Matthew Beecham lifts the lid of the VW Eos, named after the Greek goddess of dawn and wind
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Let’s start from the top
Automakers now use sunroofs and other roof systems to help differentiate the product offerings to customers. In other words, roof systems are fast becoming part of a car’s identity. The small, rectangle-shaped roof window is being outshone by more eye-catching roof designs. The design emphasis these days is less on the old tilt and slide sunroofs and more on glass roofs stretching the length of the car and smart combinations of convertible and glass roofs. Panoramic sunroofs stretching the length and breadth of a vehicle are becoming increasingly popular on both sides of the Atlantic. In fact, manufacturers report an “unbelievable” amount of interest in large sunroofs.
Hats off to Webasto
Over the past few years, novel RHT designs have enabled automakers achieve that appearance of a coupé yet with four comfortable seats. “OEMs are now able to achieve designs which are much closer to traditional coupé shapes as opposed to a two-part retractable hard-top on a four seater car which often resulted in a design with a very flat windshield,” said Andreas Weller, marketing director, Webasto Roof Systems Inc. “Today’s retractable hard-tops designs offer more design freedom, enabling OEMs to achieve the traditional coupe look with a retractable hard-top. That is a very exciting development in the convertible industry.”
Webasto worked with VW to develop a unique five-piece steel and glass roof with a sunroof mode sandwiched in between. “The VW Eos is a leap forward in convertible roof design, combining a sunroof, retractable hardtop and coupe all in one,” said Brett Healy, Vice President Business Development, Webasto Roof Systems Inc. “VW refers to the Eos as a CSC – Coupe, Sunroof, Convertible. VW / Webasto are the first to offer such functionality in a retractable roof. So that is a pretty big leap. I think that both Volkswagen and Webasto were courageous to put that vehicle into the market. It has done very well to date so the risk has paid off. As far as tomorrow’s retractable hardtops are concerned, we have additional innovations in our pipeline.”
While the Eos bears some relationship to the VW Cabrio and resembles the Golf and Passat in terms of size, VW says it is not a convertible created by removing the roof of a hard-top. Rather, says VW, it was designed from the base up to be a convertible coupé. Thomas Schuett, R&D Webasto Convertible Systems, Webasto AG, was heavily involved in the design and development of the VW Eos. Other than the traditional technical considerations of vehicle aerodynamics, structural performance, electronics and sealing surface interfaces when dealing with a convertible, Schuett told us that Webasto had four specific drivers for the roof design, namely:
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By GlobalData- Provide a full four passenger vehicle on the given platform, no compromise to the passenger compartment for a full sour passenger seating capabilities.
- Not to compromise the front header position, which was difficult to package, while guaranteeing the full convertible feel for the driver.
- Maximize luggage volume remaining in the trunk.
- Allow styling to create a nice design line of the car with a very low rear end and small rear overhang. In addition, the stylist had an emphasis on the reduction of visible gaps.
A five part guide
The roof of the Eos is the first to feature five moving pieces, including the sliding roof and takes just 25 seconds to open or close. By pressing a buckle-shaped switch located just behind the handbrake, the sunroof slides backwards (part 1) with a reassuring clunk-click as the side windows are lowered. Meanwhile, the entire rear section of the roof from the C-pillar up to the ‘imaginary’ B-pillar is lifted upwards (part 2). The sunroof then slides under the rear area of the roof forming a glass and tin sandwich. Now the hydraulic control system folds the entire roof cover compartment lid, including the lid of the boot, backwards (part 3). Then the lateral roof spars (parts 4 and 5) of the windscreen frame slide back as well. The sunroof and the rear part of the roof are completely lowered into the rear of the car, and the roof spars slide into separate cavities (covered by lids) near the rear side window. When the roof is up the Eos has a boot space of some 380 litres; the top is down 205 litres are available. The entire roof incorporates no fewer than 470 parts. The Eos offers a number of different open-air roof combinations, ranging from the sunroof open to the roof down with the side windows up to totally topless.
An eight-cylinder electro-hydraulic pump activates the CSC roof. The radial piston itself is located under the luggage compartment cover behind the spare wheel. The operating pump pressure of 160 bar is provided by a 40 amp electric motor, and is activated by a central roof control unit.
The new model’s steel folding roof, engine starting and electronics are powered by two 6 volt batteries from Varta’s sister brand Optima. These compact, lightweight SpiralCell batteries are mounted beneath the steel roof cover on either side of the car to distribute the weight. They are connected via a cable to provide 12 volt 50 amp/hour performance.
Evolutionary market
Meanwhile, the expanding convertible segment is crossing all vehicle segments. 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 new convertible concepts,” concluded Weller, “we have seen a very rapid development over the past five to ten years, particularly in Europe. Over the next few years, I expect to see more of an evolution than a revolution in convertibles. You will see refinement in the new designs to further gain packaging and trunk room efficiencies, but this in more evolutionary development. I think it is time for OEMs and the end customer to embrace and understand the benefits of the new designs.”
See also: Global market review of automotive roof systems – forecasts to 2013
