At the 1986 IAA Exhibition in Frankfurt the BMW Group unveiled its first 3 Series convertible which impressed with its enjoyable driving experience and elegant silhouette. 35 years and five generations later, the Bavarian automaker now presents the BMW 4 Series, the first four-seater convertible with panel bow roof and tonneau cover. The convertible experts from Webasto, world market leader for roof systems, were originally responsible for the roof – as they are once again today.
In terms of design, lightweight construction and acoustic comfort, Webasto combines the best features from the world of convertible roofs. By using innovative materials and sophisticated kinematics, Webasto carries the elegant look of a coupe over to a convertible top with a textile appearance.
Harmonious design
The decisive factor for achieving this shape, which has long been unattainable with fabric soft tops, is its innovative panel bow roof design. When closed, the folding roof spans the passenger compartment seamlessly in an elegant arc. The compact shape of the soft top creates a harmonious and striking coupe silhouette, both inside and out. The highlight here is the combination of panel bow elements that abut each other without joints. The soft top’s high-quality textile material, which is pulled taught over the entire roof and lies flat, shows no contours or outlines of the top’s frame whatsoever. This delivers the stability of a hardtop with the light and airy look of a textile top. It is available in two variants As an alternative to the standard black finish, the anthracite silver-effect variant lends an elegant metallic shimmer, particularly in direct sunlight.
Optimized weight
The hybrid roof of the BMW 4 Series convertible is significantly lighter than its predecessor’s hardtop Compared to a hardtop, the lightweight solution of frame and roof elements reduces the weight of the soft top by 50 percent – a value that has a decisive impact on the convertible’s fuel consumption. The panel bows have a paper honeycomb core which is sheathed with a mixture of polyurethane and reinforcing fibers. Webasto has specifically adapted this innovative paper honeycomb process (PHC) for the production of large roof outer skin components. This makes the top of the BMW 4 Series convertible especially light, while simultaneously delivering improved stability.
Aeroacoustics on coupe level
But the panel bows serve not only to enhance appearance and reduce weight, they also provide very effective noise and heat insulation. They are compact components composed of several layers. The acoustic insulation and interior headliner lamination are also integrated directly into the bows. This sandwich principle offers coupe-level aeroacoustic performance and facilitates heating of the interior at low ambient temperatures.
Light and joy of life at the touch of a button
The roof can be opened within 18 seconds while driving – at the touch of a button. In a single flowing movement the four roof elements are stacked on top of each other. At the same time, the top cover opens rearwards and the roof elements are stored underneath. This complex kinematic process leverages the accumulated technological expertise of Webasto’s Research & Development staff gained over 35 years of experience in the convertible segment. Opening and closing the top takes place quietly and efficiently with the aid of an electro-hydraulic drive. It can be operated at speeds of up to 31 mph – and also by remote control. Thanks to the clever storage system, the new soft top takes up significantly less space in the rear than the predecessor model’s retractable hardtop. This increases storage volume to 385 liters.
Technical specification of the hybrid roof:
Panel bow roof comprising 4 elements
Opening and closing time: 18 sec.
Can be opened and closed up to 31 mph
Trunk volume (irrespective of roof position): 380 l
Weight: approx. 65 kg
SOURCE: Webasto
