Under EU Directive 2015/719, truck cabs will be allowed to get longer – if this can improve aerodynamics and pedestrian safety. In the commercial vehicle segment, this change has caused quite a stir. Numerous OEMs are already working on design studies. IAV is developing its own concept that meets EU requirements and takes account of the numerous interrelationships with other disciplines.
Today, the frontal area of a truck’s cab produces a high level of aerodynamic drag. If the cab were to be lengthened, made rounder and the outside rearview mirrors designed differently or replaced with cameras, the drag coefficient could be improved and fuel consumption reduced. “Greater radii reduce the dynamic pressure zone at the front end of the vehicle”, explains Oliver Predelli, Senior Vice President for Business Development Trucks at IAV. “Newly designed outside rearview mirrors reduce the vacuum zones to the side of the semitrailer tractor. Both noticeably reduce the aerodynamic drag of propelled vehicles”.
Many applicable directives remain in force
But greater radii demand a larger front end – exactly what the new EU directive has been permitting since this year. However, the developers must bear in mind that many of the other regulations are still in force and restrict their latitude in redesigning the driver’s cab. These include the requirements on under-run protection (ECE R-93), on cab safety (ECE R-29/03) and on safety (ECE R-61). The turning circle (“BO Kraftkreis”) as stipulated by German Road Traffic Regulations also remains in effect as a criterion for permissible design. Even with a longer driver’s cab, a truck must remain within the prescribed radii (12.5 meters on the outer circle, 5.3 meters on the inner circle) when driving in a circle.
IAV’s commercial vehicle experts are aiming to develop a concept design for a new semitrailer truck that improves aerodynamics and safety while being absolutely suitable for road use. It involves lengthening the front end by 80 centimeters and shifting the front axle by 40 centimeters. This gives the engineers the latitude they need for a significantly rounder and aerodynamically optimized design. “The potential the new cab has for saving fuel will soon be shown by a model in wind tunnel tests”, Predelli says. “Particularly in combination with adaptive tail end fairings, the effect is likely to be very attractive for truck operators.”
Interdisciplinary cooperation among the technical experts
However, this involves far more than merely lengthening and rounding the driver’s cab. Many assemblies in the truck are affected by the change which is why IAV is bringing its experts together on this subject in interdisciplinary workshops. “This is about disciplines belonging to IAV’s core competencies and for which we have may experienced developers”, Predelli says. “We are discussing the new issues with them in depth.”
The new challenges start with the chassis. Does the front axle need to narrower if the driver’s cab significantly tapers in towards the front? What does this mean for the stability of trucks? And how does the steering column and system need to be designed if the driver’s position is changed? Questions also arise at body-in-white level: “To get to the engine, the driver’s cab must be tipped forward”, Predelli explains. “We must make sure that this can also be done with a longer design without the whole vehicle tipping over.”
New windshield wipers needed
On the exterior, the windshield will need to be redesigned as it will also become much rounder. This poses a quite a specific challenge: how do windshield wipers need to be designed in future for them to work reliably? Other questions include: How do the steps need to be configured in the future? And what does a longer driver’s cab mean for the design of the doors? Might they need to be positioned behind the cab? Added to these are matters of passive safety. If the windshield is set lower in future, a pedestrian could strike his head on it in a collision and be seriously injured.
“These are just a few examples of the challenges we will have to face in redesigning the driver’s cab”, Predelli says. “Further examples concern the interior – such as the question of whether the driver is to sit in the middle and what his living area is to look like.” The additional space in the driver’ cab could also be used for office work. When the truck becomes highly automated in the future, the driver could take care of correspondence on the side, for example.
Besides the technical matters, the costs will be at the focus of IAV’s developers right from the start. “The new design is only worthwhile for long-distance haulage which is why the higher cost can only be spread over a limited number of trucks”, Predelli says. “This is why we are also thinking about cost-effective production methods that will let us get the newly designed driver’s cab into volume production later on.”