Ever since Mercedes-Benz offered the first car sunroof in 1932, the ways in which vehicle makers have sought to let the sun shine into the cabin have become increasingly complex. Modern sunroofs consist of around 200 parts, and vehicle makers now use them and other roof systems to help differentiate the product offerings to customers. The small, rectangular shaped roof window is being superseded by more eye-catching roof designs.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 together with smart combinations of convertible and glass roofs.
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Wide choice of design styles
Sunroofs are available in a variety of shapes, sizes and styles. Sunroof styles typically divide into five categories:
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Pop-up sunroofs | A pop-up sunroof is a manually operated tilting glass panel. These panels are usually removable. The tilting action provides a vent in the roof, or a full opening if removed. Although the cheapest in the range, the downside is that a pop-up does not have a sunshade – a ‘must have’ feature for driving in warmer climates. | Typically an aftermarket product, pop-ups retail from between $200 to $650. |
Top mounted sliding sunroofs | The top mounted sliding sunroof features a glass panel that slides open and is stored in the tracks on top of the roof, avoiding loss of headroom. They have been a popular factory-fit item in Europe for some time. Most feature an integral wind deflector to eliminate wind noise and add to the European styling. | n/a |
Tilt and slide sunroofs | Tilt and slide sunroofs combine the features of a pop-up with those of a top mounted sliding sunroof. They tilt to vent and slide open above the roof. Although they do not offer quite as large an opening as other sunroof types, the convenience of sliding open a pop-up instead of removing the panel can be a desirable feature. Most are power operated, with optional features such as integrated sunshades and electronic control modules. | On the aftermarket, retail prices range from $500 to $800. |
Internal sliding sunroofs | Internal sliding panel sunroofs are usually electric and often factory-fitted options in luxury vehicles. The panel slides open between the metal roof and interior headliner, resulting in some loss of headroom. The panel slides to provide a full opening in the roof. Advantages include push-button open/close and a self-storing panel. | Retail prices for OE and aftermarket installations range from $1,000 to $1,400. |
Folding sunroofs | The folding sunroof offers the convenience of a sunroof with an opening more like a convertible. Unlike other sunroofs, the panel (cover) for the folding sunroof is made of cloth (or vinyl), which folds back as it slides open. | Retail prices range from $700 to $1,400. |
Source: Company reports and industry estimates
Tilt and slide sunroofs still the most popular
In the US, industry sources reckon that tilt and slide sunroofs account for around 70% of total sunroof production, pop-up sunroofs account for around 15% (mainly aftermarket), followed by the spoiler type and others.
Complex structures
Whatever the version, sunroofs are by no means simple mechanisms. They contain up to 200 parts and yards of wiring. Any problem in noise or water leakage can turn it into a nuisance because of its proximity to the driver’s head.
Larger and more stylish sunroofs
Sunroofs are getting larger and more stylish. The large roofs and panorama roofs that can be seen in current vehicles such as the Renault Avantime, BMW Mini and DaimlerChrysler’s C-class sports coupé show the direction in which sunroof development is taking.
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In the US, Mark Pauzé of ASC Inc says there are a number of consumers who want the delights of a convertible without losing the rigidity of a hard top. He said: “It’s interesting to look at the territory between a traditional sunroof and a traditional convertible. In the SUV segment, for example, we have found that North Americans want more light and air, but don’t want that to conflict with the functionality of the vehicle. We’re finding interesting configurations of open air that are beyond the traditional sunroof but not as open as a convertible. On one side, there are the die-hard convertible owners. But there are a lot of people on the fringe of that who want something more open but they still want to have a trunk and a back seat. They feel vulnerable in a convertible. So, there are other ways that we are looking at to open up a vehicle but still maintain a four-door vehicle, trunk space and yet still have more structure to the vehicle than a traditional convertible. Although that is appearing in Europe now, you won’t see it taking off in the US until around 2005.”
Both Audi and Mercedes-Benz have introduced wide-aperture sunroofs that offer larger openings and entire roof panels of glass to create a light and airy cabin environment. The Audi package called Open Sky System can be seen on the A2 and was developed and supplied by ArvinMeritor.
The Open Sky System uses a total of four glass panels. The retractable glass roof runs the entire width of the car, extending as far back as the tailgate window, and is an optional extra for the new Audi A2. The front and rear are fixed, while the centre pair tilt and slide over the rear panel to form a stack. Audi demanded that the A2’s curved roof profile remain unbroken by unsightly split lines, and to achieve this ArvinMeritor incorporated 12 WITOL adjustable nuts into the system. Every unit is individually adjusted during manufacture to ensure that the fit of each panel is no more than two millimetres below the panel in front. Audi hopes this ‘Open Sky’ system will boost its declining sunroof operations.
The latest Mercedes-Benz C-class sports coupé is fitted with a panoramic sliding sunroof for plenty of fresh air and light in the interior: from the front windscreen through to the rear spoiler, everything is glass. Just press a button, and the front half of the roof glides towards the rear, leaving a roof opening that is about a third larger than a conventional sunroof. The glass panel in front of the sliding roof flips up to act as a wind deflector. Two electrically operated roller blinds on the inside of the roof protect the coupé’s interior from direct sunlight. Webasto designed this Panorama roof. The German supplier started working with Mercedes-Benz in 1997 when development of the sports coupé began. The C-class sports coupé is aimed at attracting both younger drivers and women to the Mercedes-Benz brand. Webasto’s novel roof design is a key element of the car’s design. The roof system is supplied just-in-time to DaimlerChrysler’s assembly plant in Stuttgart.
Renault’s Avantime model features a one-square-metre sunroof (the industry’s largest). Renault says the combination of this sunroof opening and the lack of a centre pillar gives an unprecedented amount of light in a closed car cabin. An ‘open air’ control simultaneously opens the windows and sunroof “creating those feelings generally found only in a cabriolet”. It is certainly true that with all four windows wound down and the large glass sunroof opened, the Avantime is almost like a cabriolet and the impression is increased by the absence of B-pillars. For those times when the sun becomes too much, the sunroof glass incorporates an infra-red filter and there is a reflective windscreen, air conditioning with dual zone temperature control and a solar radiation sensor. The sunroof was designed, developed and manufactured by Webasto. The Avantime is based on the current Espace platform and is built for Renault by Matra in France.
Peugeot has designed the new 307 SW as a leisure-oriented and MPV-influenced version of its upcoming 307 estate car, giving it a panoramic glass sunroof, seating for seven and plenty of interior storage compartments including under-seat trays and drinks holders.
Citroën has also introduced a full-length sliding glass sunroof on its new C3. Citroën says it is aiming at a very wide range of potential customers (mainly young people, either single or with families) and expects to sell 160,000 units in 2002, 54,000 of them in France alone, with sales rising to 334,000 in 2003. The company reckons it has a winning formula with the C3, with a rounded and cheerful shape and a spacious and light interior, plus an option of a full-length sliding glass sunroof. The company is positioning the C3 between the Saxo and Xsara, and it is not a replacement for either model.
Webasto’s two-panel sunroof is also an option on BMW’s Mini Cooper. This has a slightly forward-sloping roof line with ‘glass walls’ disguising load-bearing A-, B-, and C-pillars. The two glass panels serve as glazing for a full roof module and the roof system is operated by an electric motor. Both left and right sides of the glass panel carry two mechanisms and two attachment points. The outer sliding roof, which is installed from inside, also features two mesh-material, manually operated sunshades for the front and rear passengers.
Smart sunroof glass
There have recently been some significant developments in light reactive windows. US-based Research Frontiers Inc has developed a light control technology, known as SPD (Suspended Particle Device) for controlling light in vehicles. A thin film is sandwiched inside the glass that conducts a low voltage of electricity. As a current passes through it, masses of suspended particles join together or disperse, allowing more or less light to pass through.
Auto applications include sunroofs, sunvisors, rear-view mirrors, instrument panels and navigation systems. It means that you can simply turn a dial to block out the light, eliminating the need for a sliding shade panel altogether. That is important for the sunroof makers as they move towards offering ‘open sky’ roof designs.
Compared to other transparency control devices?such as electrochromic or liquid crystal?SPD is cheaper per square foot and reacts faster. “Not only do we have a cost and speed advantage,” says John Tobias, Director of Automotive Marketing for Research Frontiers, “but with SPD, you can precisely tune an entire range automatically or manually. It can be totally dark, totally bright or somewhere in between. Electrochromic technology can still be tuned but not to the extent that SPD can. Another advantage is that SPD is a film. It can be shipped all over the world. So you can have glass waiting at any factory on a global basis and the film can just be shipped to that factory, unlike electrochromic.” In the default state, with the power off, the window is dark and would not be able to form the main component of a windscreen. Perhaps the upper band strip but not the entire windscreen. But when a motorist parks their car, SPD would be in the ‘off’ state, an advantage for sunroof applications.
According to Tobias, there are around 6.2 million sunroofs manufactured globally, or 11.6% of the estimated 53.8 million cars and light trucks produced annually. Sunroof penetration rates have been growing steadily, and some industry leaders expect the percentage of vehicles with sunroofs worldwide to grow to 50% over the course of the decade.
There are plenty of licensees for this technology, too. Research Frontiers include Glaverbel, Global Mirror, Hankuk Glass Industries and AP Technologies as licensees. Asahi Glass’ North American subsidiary, AP Technoglass, recently bought the global non-exclusive rights to manufacture SPD sunroof glass.
