To further reduce fuel consumption in truck/semitrailer combinations, Daimler launched its “Aerodynamics Truck & Trailer” initiative. As part of this, engineers researched the aerodynamics of current vehicle concepts and then developed two innovative and at the same time practicable solutions.

The solutions are relatively easy to put in place in the short term. Last year, the tractor/trailer combination was a spectacular design study, this year it is already a reality: with the new Mercedes-Benz Aerodynamics trailer, a long-haul tractor unit can save approximately 2000 litres of diesel annually, thereby saving its operator nearly 3000 euros in expenses. At the same time, the environment is spared more than five tonnes of CO2 emissions each year. The second vehicle, the Mercedes-Benz Aerodynamics truck, is a rigid truck for long-distance haulage and short-radius distribution operations. It saves between 300 and 600 litres of diesel annually and up to 1.5 tonnes of CO2. The Aerodynamics trailer and Aerodynamics truck will celebrate their world premiere at the International Motors Show for commercial vehicles (IAA) at the entrance to Hall 14/15.

Air resistance falls by 18 percent, consumption by 4.5 percent
From the vision of the 2011 study, the trailer has become a reality in 2012. The Aerodynamics trailer designed and developed by Mercedes-Benz lowers the air resistance of the entire tractor/semitrailer combination by approximately 18 percent. According to the engineers’ experience, this results in a fuel consumption reduction on long-haul journeys of approximately four to five percent in real conditions. Intensive measurements in the wind tunnel with a 1:2.5-scale model confirmed the arithmetic assumptions.

In the next step, real-world tests conducted by Mercedes-Benz on the road proved that a tractor/semitrailer combination with a gross weight of 40 tonnes consisting of a Mercedes-Benz Actros – currently offering the best aerodynamics in a series production truck – and the aerodynamically optimised Aerodynamics trailer can achieve fuel savings of 4.5 percent in long-haul usage. In the case of an average annual mileage of 150,000 km for a long-distance truck, this means a reduction in diesel consumption of around 2000 litres and relieves the burden on the environment by more than five tonnes of CO2 annually. In real terms, trucks which are subject to toll charges on German motorways (12 t and above) cover around 25 billion kilometres which corresponds to 300 million litres of diesel that can be saved in a year, as well as over 800,000 tonnes of CO2 emissions.

Actros StreamSpace tractor unit remains unchanged
The tractor unit, here the new Mercedes-Benz Actros with StreamSpace cab, remains unchanged. The new Actros is already aerodynamically optimised. It will merely be equipped with an air deflector on the roof, cab side deflectors and side trim panels between the axles. This aerodynamics package is already available ex factory for heavy-duty Mercedes-Benz trucks in long-haul transport.

Aerodynamics trailer ready for everyday use – with no restrictions
Not just some futuristic concept, the Mercedes-Benz Aerodynamics trailer is ready for everyday use, without any restrictions. It is based on a conventional 13.6 m freezer box body, with a refrigeration unit at the front end. Whether for ground clearance, approach/departure angle or ease of loading at the rear – the Aerodynamics trailer meets all the usual requirements of everyday haulage. The box body remains unchanged despite the aerodynamic measures.

The development partners in the IAA project were Daimler Trucks and renowned trailer specialist Schmitz Cargobull. They ensured focus was on everyday suitability. Working closely with designers and engineers from Daimler Trucks, Schmitz Cargobull developed the attachments on their own, based on designs furnished by Mercedes-Benz. These were transformed by Schmitz Cargobull into the actual Aerodynamics trailer using computer surface data.

Generally speaking, however, the Aerodynamics trailer is not bound to a particular brand: as it had done at the “Trailer” show in Kortrijk in autumn 2011, Mercedes-Benz once again invites all trailer manufacturers to develop efficient, environmental semitrailers on the basis of the Aerodynamics trailer.

Based on a design study from Mercedes-Benz
The Aerodynamics trailer began as a study presented by Mercedes-Benz last autumn at the “Trailer” trade show in Kortrijk, Belgium. Going beyond the Actros, Mercedes-Benz had set its sights on the entire tractor/semitrailer combination.

By way of background, with the new Actros, Mercedes-Benz has introduced the most efficient heavy-duty truck. It proved this in the spectacular Actros Record Run covering 10,000 kilometres on European motorways: the Euro VI version of the Actros 1845 achieved a fuel consumption of only 25.9 l/100 km. Both customer reactions and the latest press trials have confirmed this excellent performance: the new Actros is the most frugal and thus the most environmentally-friendly truck in its class.

There are many reasons for this. The new Mercedes-Benz Actros has a completely redeveloped, fully automatic powertrain, revolutionary assistance systems such as the GPS-controlled Predictive Powertrain Control (PPC) cruise control system and last but not least, after 2600 hours in the wind tunnel, a sophisticated aerodynamic design. This leaves little room for further significant fuel savings accomplishments in the near future.

As the Aerodynamics trailer shows, ultimate efficiency in a semitrailer is only achieved with the perfect combination of tractor unit and trailer. Based on the results of the Record Run, a realistic fuel consumption of less than 25 l/100 km is possible for a 40-tonne tractor trailer when a Mercedes-Benz Actros is combined with an Aerodynamics trailer. Just a few years ago, experts in the field would have dismissed such figures as utopian.

Not just a show vehicle but a realistic semitrailer
The designers and developers from Mercedes-Benz did not rely on unrealistic show effects when combining the new Actros with the Aerodynamics trailer: this vehicle combination is producible, upholds the framework of coming legal requirements and is absolutely realistic for everyday use under tough road transport conditions.

No change in refrigerator box body dimensions
The Aerodynamics trailer at the IAA corresponds largely to the Mercedes-Benz study. The basic model is a refrigerator trailer, a typical vehicle for long-distance haulage. Measuring 13.6 m long and 2.6 m wide with a total height of 4 m including the chassis, the familiar box body remains unchanged for the Aerodynamics trailer.

Spoilers, trim panels and diffusers lower wind resistance
Numerous individual measures on the Aerodynamics trailer lower the air resistance of the entire tractor unit. A spoiler on the bulkhead of the trailer reduces the distance to the tractor unit, and this itself lowers air resistance by one percent. The spoiler frames the refrigerator unit, with air slots providing the necessary ventilation.

Meanwhile, the plastic side trim panels on the Aerodynamics trailer contribute an eight percent improvement to the air resistance. As in the design study, they are slightly drawn-in at the front and characterised by an opening at the rear. This steers the air in the direction of the striking rear diffuser.

The diffuser has the shape of a parallelogram and links up with the underbody panelling. Also made of plastic, it improves the wind resistance by a further one to two percent.

The diffuser surrounds the rear underride guard and serves as a mount for the tail lamps. Accentuating the striking Aerodynamics trailer at night are round tail lamps, instead of the multiple compartment lamps typical of the brand. They emphasise the almost sporty design of the Aerodynamics trailer. The elaborate trim panels on the lamps underline the detailed aerodynamic touches. The same is true for the trim panels of the landing legs beneath the body.

Saving the best for last: the rear taper of the Aerodynamics trailer

An important component of the complete aerodynamic system is the “boat tail”, a rear taper measuring up to 400 mm in length. It improves the air resistance of the entire tractor unit by a full seven percent. Its elements can be folded away, ensuring the usual easy access to the cargo compartment. The wings of the rear taper are made of aluminium sections and the sides are elegantly curved.

Practicable down to the last detail
The developers of Mercedes-Benz and Schmitz Cargobull paid particular attention to the everyday usability of the Aerodynamics trailer. Its rear aerofoil automatically swings approximately ten degrees upwards during loading and unloading, providing clearance for the doors of the loading portal. When the trailer unit is stationary, electric actuators automatically fold the side wings of the taper onto the door sections. This ensures an opening angle of around 245 degrees when opening up the doors.

It also enables the trailer to negotiate bollards when manoeuvring at loading/unloading docks and to dock at the loading bay for loading and unloading. Even the familiar buffers at the rear are a mark of practicality.

A ground clearance of 350 mm for the side trim panels and the approach/departure angle of the Aerodynamics trailer likewise correspond to the requirements of companies, important for example when negotiating ferry ramps. Engineers and developers also focussed on easy accessibility of the landing legs as well as operation of the control valves and easy operation of the loading portal. A practical pallet box is provided, as are the required side marker lamps.

The hinges on the loading portal are standard parts, as too is the frame structure of the side trim panels. In other words, it will soon be possible to manufacture the Aerodynamics trailer on a commercial scale.

Future EU length regulation allows rear taper
An essential element of the Aerodynamics trailer is the “boat tail” with a rear taper in the form of flaps. These extend the Aerodynamics trailer by 400 mm and are more important for the aerodynamics of a tractor/semitralier combination than unrealistic nose-shaped cab extensions.

Appeals to this effect to lawmakers for a modification of the length regulations did not fall on deaf ears: in May of this year, the EU Commission recommended an extension of the maximum length by up to 500 mm for aerodynamic measures at the rear. Prerequisites: the loading length must not be restricted; when the vehicle is stationary, the extension must fold in to the permitted maximum length of 16.5 m for semitrailers and must not adversely affect use in combined operation.

The Mercedes-Benz Aerodynamics trailer meets these requirements. The flaps on the rear extension fold in automatically by means of an electric motor when the vehicle is at a standstill. This does not impair the vehicle’s manoeuvrability. It is anticipated that the change in length regulations in the EU will become law by early next year.

Aerodynamics truck lowers fuel consumption by three percent
An aerodynamically optimised rigid truck in long-haul transport and short-radius distribution also relieves the burden on the wallet and the environment, as evidenced by the Mercedes-Benz Aerodynamics truck prototype. In this project the aerodynamic engineers and development engineers at Mercedes-Benz took ideas from the Aerodynamics trailer and applied them to the rigid truck, with vehicle-specific enhancements.

Rigid vehicles can also achieve considerable potential savings: there is a large number of aerodynamically relevant applications even in short-radius distribution. Thus the new Mercedes-Benz Antos was used as the basis vehicle and then developed to offer the best aerodynamic figures possible. Added to this are typical long-haul applications such as furniture or flower transport. This is also true for toll-free rigid vehicles under the 12 t permissible gross weight rating.

Compared with conventional box-type rigid vehicles, the Aerodynamics truck improves aerodynamics by approximately twelve percent. This means a consumption reduction of approxi­mately three percent on trunk roads. In the case of an annual mileage of 50,000 kilometres, this results in a saving of around 350 l per year, equivalent to a saving of around 500 euros for the operator or just under one tonne of CO2 for the environment. With higher mileages in long-haul transport, the prospects of the Aerodynamics truck are even more favourable.

These projections from the development engineers have been confirmed in practice in initial test drives.

Basis of the Aerodynamics truck: chassis plus ClassicSpace
The basis of the Mercedes-Benz Aerodynamics truck is a two-axle platform truck chassis with 18 t permissible gross weight rating and the 2.3 m wide cab of the Actros ClassicSpace. A cab from the new Mercedes-Benz Antos is also available. Particularly in short-radius distribution, this vehicle sets standards and is available in two cab lengths.

The same goes for the Aerodynamics truck: good aerodynamics is a standard feature of the cab. The cab side deflectors are from the tried-and-tested accessories range from Mercedes-Benz and fit almost flush with the structure. There is no need for a spoiler on the bulkhead, but the air deflector on the roof is necessary.

Box body: smooth walls, rounded edges

The body is a conventional box with an outside length of 6.5 m, a width of 2.55 m and an inside height of 2.20 m. The outer skin is made of smooth Alucobond plates, which provide little resistance to the wind. In contrast to many aerodynamically unfavourable box bodies, the Aerodynamics truck has an edge radius of 80 mm at the transition of the side walls to the roof and an edge radius of 200 mm at the bulkhead. This ensures a streamlined airflow.

The side trim panels are reminiscent of the Aerodynamics trailer. Their upper edge fits nearly flush with the box body. On the Aerodynamics truck as well, the trim panels at the rear are drawn in and direct the air towards a rear diffuser, which fully encompasses the underride guard. An edge radius of 200 mm at the bottom end of the side trim panels provides a soft transition without separation of air flow towards the underside.

The entire underside of the Aerodynamics truck is covered in panelling. The almost entirely closed body this creates approximates the aerodynamic ideal and is interrupted only by slots for dissipating heat from the engine.

“Boat tail” conceals a tail lift

Amongst the outstanding features of the Aerodynamics truck from any perspective is the rear portal with a “boat tail”, a taper similar to the Aerodynamics trailer. The folding elements of the portal are largely the same as those of the Aerodynamics trailer. In this case, however, the spring-actuated elements fold open as needed towards the side, since a tail lift behind the flaps provides access to the load compartment.

The Aerodynamics truck is also fully ready for everyday use
As with the Aerodynamics trailer, practicality for everyday use is of utmost importance in the Aerodynamics truck as well. For example, the side trim panels can be folded away, providing easy access to the fuel and AdBlue tank for instance, as well as to the rear wheels. The ground clearance and approach/departure angles also meet the requirements of everyday use.

The body of the Aerodynamics truck was developed and produced by Daimler Trucks. While the work was under way, the engineers implemented a further idea: the operating panel for the loading tailgate is integrated into the side wall and can be easily operated from a standing position.

Further measurements and customer driving tests
Development of the Aerodynamics trailer and Aerodynamics truck will not end with the presentation of the prototypes at the IAA. Further extensive consumption measurements and driving trials will be conducted this autumn by the vehicle testing division at Mercedes-Benz. In the next step, selected customers will test the Mercedes-Benz Actros and Aerodynamics trailer combination in everyday haulage operations.

The same is true for the Mercedes-Benz Aerodynamics truck. It, too, will first undergo thorough testing as a laboratory vehicle. If there is sufficient demand, the Aerodynamics trailer and Aerodynamics truck will be able to be transitioned to large-scale production relatively quickly. Also conceivable are extensions to the Aerodynamics truck by means of an appropriately equipped trailer, thus creating an Aerodynamics truck/semitrailer combination.

Good aerodynamics thanks to extensive experience
There is a long tradition of adopting a holistic approach to the truck and trailer at Mercedes-Benz. Even back in the mid-1980s the development engineers were carrying out in-depth investigations into the aerodynamics of entire truck/trailer combinations. These involved research into the effect of air deflector panels, side trim panels, edge radii and rear end tapers. Of inestimable value for testing even then was the company’s wind tunnel located at the plant in Stuttgart-Untertürkheim, directly adjacent to the Development department.

The fundamental knowledge gained back then is still valid to this day and forms the basis for the current investigations. In those days the focus was merely on saving fuel for economic reasons; priority had not yet been given to protecting the environment by reducing CO2 output. Today, some 25 years later, environmental relief, conservation of resources and improved economy represent seamless additions.

The significant aerodynamic improvement of 17 percent which occurred with the model change from the Mercedes-Benz SK to the first-generation Actros in 1996 can be attributed to the basic research of earlier development generations. Further improvements of around 4 percent were achieved during its lifetime.

A jump of approximately ten percent occurred with the model change to the new Actros. The precondition for this was intensive development work on the computer and in the wind tunnel. Basic investigations began in 2001, a full ten years before production launch. They continued with styling studies in 2004 and one year later with an initial full-sized cab prototype. The work in the wind tunnel added up to 2600 hours in all, in which every detail was closely examined.

Source: Daimler AG