• The Mercedes-Benz Unimog clears roads when other vehicles can’t get any further
• Winter maintenance is a core competence of the Universal-Motor-Gerät (universal motor machine) early on
• Mercedes-Benz Museum Close-Up: Cars, Architecture and
  Exhibition Design – No. 1/2022

Stuttgart. “Close-Up” – the name of the series by the Mercedes-Benz Museum says it all. Each instalment tells surprising, exciting, profound stories. To do this, it shines a spotlight on details of a vehicle, exhibit or element of architecture and design. In the spotlight this time: the Unimog U 500 as a winter road service vehicle from 2004.

No. 1/2022: Mercedes-Benz U 500 winter road service vehicle, 2004

A real all-rounder: Snow blower at the front, heavy snow chains on all four wheels and a spreader at the rear: the Unimog U 500 of the model 405 series in the Mercedes-Benz Museum would be well prepared for harsh winters – it shows this to the viewer from all sides. But the 2004 implement carrier with portal axles and all-wheel drive could also work in the field, tow trams or carry out mowing work. For as spectacular as its individual performances are, the Universal-Motor-Gerät (universal motor machine – that’s what the abbreviation Unimog stands for) is admired even more for its versatility. This is made possible by compatibility with a wide range of attachments that can be mounted and driven at the front, rear and centre of the vehicle. If you look closely at the exhibit in the Museum, you will see the many connections for the hydraulic system. The attachments also include various solutions to keep roads passable even during heavy winter snowfalls.

Traditional winter king: Winter service under adverse conditions is practically in the Unimog’s genes: The all-rounder, which has been in production since 1949, was originally developed for agriculture. Because of its wide range of applications, however, it was also used for winter maintenance from the 1950s onwards – with a snow plough or snow blower as an attachment, the Unimog became the winter king. Both clearing techniques still play an important role in winter service today. In addition, there are rotating roller brushes for small amounts of snow and various spreading methods for de-icing salts or gritting materials.

Pushed, not flung: A snow blower and snow thrower – like the ones on the Unimog on display in the Museum – has a more elaborate technique than the snow plough. Any homeowner who has to clear the pavement in winter can understand this: a few centimetres of powder snow can easily be moved to the side with the pusher. Picking up and shovelling away larger amounts of snow, on the other hand, requires a lot of strength and several work steps. The viewer can also sense the high performance of the exhibit when they see the robust construction of the blowing machine and the many hydraulic hoses for driving various units.

Tossing the snow far and wide: The chimney of blue-painted sheet metal rises high above the snow blower in the Museum, the top of the channel shaped into an ejector. The message is clear: the snow is not only picked up, but also thrown to the side in a high arc. This is indispensable for large snow depths, which also occur in Germany in low and high mountain regions. This is because the considerable volume of frozen precipitation cannot simply be pushed to the side. Snow blowers therefore throw it up to 35 metres away from the road.

Powerful through the winter: A modern mounted snow blower like the one in the Mercedes-Benz Museum is driven by the vehicle engine via a power take-off shaft and is also controlled via several hydraulic lines. The black hoses are clearly visible on the 205 kW (279 hp) exhibit in the Museum with its 6.4-litre six-cylinder engine. From the 1950s onwards, the first Unimogs with powerful snow blowers generally had a second engine in addition to the vehicle drive. This usually also came from Mercedes-Benz, was located in the rear of the vehicle and drove the blower at the front from there via a shaft.

Cutting, blowing, throwing: Rotary snow blowers clear the snow in several work steps. Viewers standing directly in front of the Unimog in Collection Room 3: Gallery of Helpers can recognise the corresponding components: two round snow blades sit on the sides of the cutter drum, delimiting the working area with a clean cut. Two spiral-shaped cutting spirals with sawtooth cutting edges are attached to the inside. These shred even large amounts of snow and bite their way through hardened or icy layers. The cutting spirals transport the material to be cleared to the centre of the attachment according to the principle of the Archimedean screw. Here, the impeller located behind the cutter drum takes over in its cylindrical housing. It accelerates the crushed snow and ejects it upwards through the chimney to the side. This can be turned hydraulically by up to 275 degrees and its tip can be set at different angles – also hydraulically. In this way, the driver determines exactly where the Unimog throws the cleared snow.

Plough and blade as standard: Snow blowers are not necessary in all regions. Municipalities and road authorities in temperate latitudes such as Germany mostly use single- or multi-blade snow ploughs or snow clearing blades as standard equipment for their winter service vehicles. Often, the road is simultaneously gritted with de-icing salt to prevent icy roads. Both systems can be optimally mounted on the Unimog.

Fighting the slipperiness: Such a spreading system for de-icing salt is mounted on the rear of the Unimog in the Museum. Salting is one of the most important methods of winter service; it removes or even prevents ice on road surfaces caused by snow and freezing conditions. De-icing salts have been used in Germany for winter service since the 1950s. Used is either commercially available rock salt (sodium chloride) or calcium, magnesium and potassium chloride. The salts combine with the frozen water and lower its melting point. This keeps the road surface grippy even at temperatures below zero degrees Celsius. Modern winter service vehicles know exactly how much of each de-icing material is needed. To do this, they measure surface temperatures without contact (thermography), and in some cases information on road and terrain conditions from databases is also incorporated into the control system (telematics). To operate the winter service technology, there is a separate control unit with a screen in the cockpit of the Unimog.

It’s all in the mix: Today, road services rarely use dry salt granulate exclusively. Instead, spreading systems can apply so-called pre-wetted salt. This is a mixture of salt crystals and a liquid brine solution. The unit mixes both components directly on the vehicle as required, and the spreading disc at the rear applies the pre-wetted salt in exact doses. The advantages: the mix works faster than dry granules, so less salt is needed. In addition, the wet salt adheres better to the road surface, which reduces the chemical load on the vegetation next to the road. Depending on the mixing ratio of salt to brine, FS 30, FS 50 or FS 70 is spread in winter, for example. The number represents the proportion of brine in the mixture. If pure brine is used, winter maintenance experts speak of FS 100. However, this is not applied with the classic spreader, but sprayed with nozzles. The right carrier vehicle for this application? A Unimog, of course.