Daimler Dernburg-Wagen, 1907.
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The ‘Dernburg-Wagen’
Aug 2, 2011
The 1907 vehicle: Not only all-wheel drive but also all-wheel steering
A highly sophisticated design by Paul Daimler
Used in colonial German South-West Africa, now Namibia
When placing its production order at the beginning of the last century, the German Colonial Office knew precisely what it was entitled to expect from Daimler-Motoren-Gesellschaft (DMG): a reliable vehicle that would withstand long journeys on unmade roads without complaint, while offering the flexibility that the motor vehicle had already amply demonstrated by the beginning of the last century. The engineer Paul Daimler, son of the company’s founder, was chiefly responsible for the design of the new vehicle, which was finally built as a one-off at the factory in Berlin-Marienfelde in 1907. This all-wheel-drive vehicle was based on a DMG commercial vehicle chassis, and had a wheelbase of four metres with a track width of 1.42 metres. The ground clearance of 32 centimetres was not unusually high for the time, as almost all vehicles were often used on heavily rutted unmetalled roads. In 1908 the publication Allgemeine Automobil-Zeitung (AAZ) said the following about Daimler’s design: ‘All significant road obstacles can be overcome by the robust front and rear axles, and the particularly vulnerable lower section of the gearbox housing is protected by a strong steel guard between the pressed frame cross-members, which is resistant enough to allow grounding of the entire frame.’
The vehicle came on the market for a price of 34,750 Marks. It was fitted with a touring car body having two seats on the chauffeur’s bench and four seats in the rear. Only the rear passengers had doors, and large steps were provided to overcome the entry height of around one meter. Extending almost to the front end and mounted on eight poles, a sunshade prevented the driver from being dazzled even when the sun was low. A luggage rack was mounted on the back for cases or spare tyres, with a further, large luggage rack on the roof protected by a tarpaulin. Awnings were affixed below the roof on both sides; these could be lowered to enclose the body and protect the occupants from wind, weather, and sand. ‘To be sure, this Mercedes is not remarkable for its light and elegant construction; on the outside, too, the evidence of power and endurance is unmistakable,’ wrote the AAZ, however: ‘The overall impression of the vehicle has not suffered as a result of the special requirements.’
With a length of around 4.90 metres and a height of a good 2.70 metres including the roof structure, the majestic vehicle weighed around 3.6 tonnes when fully equipped with all the items specified by the Colonial Office, such as a particularly heavy-duty clutch, petrol and coolant reserves for tropical conditions, replacement parts and tools.
Despite this, the four-cylinder engine performed manfully, delivering a very respectable output of 35 hp (26 kW) from a displacement of about 6.8 litres at 800 rpm – allowing a maximum speed of around 40 km/h on level tarmac. In view of the intended operating conditions, however, a more important factor was its climbing ability of 25 per cent made possible by the all-wheel drive.
The vehicle featured permanent all-wheel drive, the engine delivering its power to the four wheels via a sophisticated mechanical system. A shaft connected it to the centrally installed gearbox, which had four forward gears and one reverse gear. From there prop shafts transferred the torque to the front and rear axle differentials, which in turn used bevel gears to split and transfer it to the wheels.
Designer Paul Daimler took special precautions to keep airborne sand out of the drive components. Many of the joints were packed with lubricating grease to keep sand at bay and prevent rapid wear, but the front axle proved to be a real challenge at first: owing to the expected heavy impacts and fine airborne sand, it was not possible to use conventional protection for the bevel gears on the wheels, a telescopic system that followed steering movements. Instead Daimler shrouded the vulnerable components with a robust, cylindrical sleeve. But since this solution limited the maximum steering angle to just 23 degrees, the vehicle was also equipped with steered wheels at the rear to achieve a reasonable turning circle. The rear wheels were also encapsulated as a protection against airborne sand. One positive side-effect was that front and rear axle components, including the differentials, wheels and brakes, were of identical construction, which considerably simplified supply of replacement parts.
The solid steel wheels also served to protect the mechanical components and drum brakes against soiling; wheels with wooden (and more rarely steel) spokes were usual at the time, however, these would have let sand into the drive components. Moreover, spoked wheels would have made it practically impossible for the vehicle to free itself after sinking into the sand. The steel wheels were shod with size 930 x 125 pneumatic tyres, another unusual feature as solid rubber tyres were still in widespread use at that time. Presumably Paul Daimler made this choice to assist the robust leaf springs in their work in view of the vehicle’s weight. Not unusually for the time, only the rear tyres carried a tread while the front tyres had a smooth surface. The tyre valve was located on the inside of the wheel so it was not so exposed to damage.
The cooling system was specifically configured for the tropical climate, with a larger cooling surface, a larger cooling mantle around the cylinders and more coolant – the circuit contained 140 litres in total. In addition to the radiator at the front end, a second radiator was mounted on the front bulkhead, enclosing it in horseshoe fashion and extending its honeycomb structure into the slipstream. Both radiators were connected via two side-mounted water reservoirs, and the heated water had to pass through all the lines and tanks before flowing around the cylinders again. ‘Even in deep sand at only 8 km/h, the cooling system performed admirably during a one-hour endurance test,’ the AAZ reported.
In late March/early April 1908 the colonial vehicle was subjected to a thorough, 1677-kilometre trial in Germany. The route ran from Berlin-Marienfelde to Stuttgart-Untertürkheim and back. Untertürkheim was reached during the morning of the fourth day, and four days after that the car was back in Marienfelde. The route included off-road sections, too, so as to test the all-wheel drive. ‘A turn in a deeply ploughed field with a gradient of five to ten per cent was negotiated impeccably,’ a Colonial Office report stated. ‘Near Wittenberg the vehicle was driven into a sandpit, in which it sank well up to its axles in the sand, but from which it managed to free itself with ease despite gradients of 20 and 21 per cent.’ In the Thuringian Forest ‘a hill approximately 150 metres high was climbed on stony, twisting, narrow roads with gradients of up to 20 per cent without difficulty. Even the steering, which was inherently cumbersome as a result of the four-wheel drive, proved itself.’ The Colonial Office’s test report was positive.
In May 1908, the vehicle was shipped to Swakopmund in Africa on board the ‘Kedive’. The Secretary of State at the German Colonial Office, Bernhard Dernburg (1865-1937) received it for his personal disposal in German South-West Africa one month later. His task was to coordinate and improve relations between Germany and the colonies. As a result of his travels the all-wheel-drive vehicle was nicknamed the ‘Dernburg-Wagen’ many years later. At the same time, these trips served as a general test of the motor vehicle as a means of transport in the colony, and to this purpose the all-wheel-drive ‘Dernburg’ was accompanied at least some of the time by other, rear-wheel-drive vehicles from Benz and Daimler, namely a seven-seater, largely armoured car from Benz and three trucks from Daimler.
The author of a travel report from that time described a journey with the Dernburg as follows: ‘The 600-kilometre trip from Keetmanshoop via Berseba to Gibeon and then from Maltahöhe, Rehoboth to Windhoek was made in a journey time of four days without accident. This is an enormous time-saving, since for the same journey an accomplished rider takes twelve days on horseback […].’ And the official was even able to use a mobile communication aid, too: ‘When [the vehicle] was carrying Secretary of State Dernburg, it also carried a field telephone that could be tapped into telegraph wires anywhere along the route.’
Following this trip, the car was made available on a permanent basis as a means of transport for the police in German South-West Africa. A precise log was also kept, showing for instance that by the beginning of 1910 the vehicle had covered around 10,000 kilometres.
The car’s driver, who also doubled as its mechanic, was sent by Daimler-Motoren-Gesellschaft along with the vehicle – common practice at the time. And since it belonged to the police, without further ado driver Paul Ritter was made a policeman. Following Dernburg's departure, Ritter remained in the country to look after the car, repeatedly returning to Marienfelde to acquire the required spare parts, as well as the repair and maintenance skills to go with them.
The details known about the ‘Dernburg’ all point to the engineering ability of Paul Daimler, who tailored the car’s design precisely to its intended application. Every single feature was thought through, so that the vehicle made no compromises with regard to its chief purpose – driving over difficult terrain.
Despite this, the journeys undertaken with the car did not always go as smoothly as those involved would have liked. This was because excessive weight, due in large measure to the Colonial Office’s special requirements, meant the pneumatic tyres were subjected to a lot of punishment. As a result, particularly in view of the significant off-road driving required, tyres lasted only a comparatively short time – 36 tyres and 27 inner tubes were used up in the aforementioned 10,000 kilometres covered by early 1910. Experiments with solid rubber tyres proved unsuccessful, since they were soon destroyed by the forces acting on the wheels.
The all-wheel drive, by contrast, proved its worth particularly on sand, on which the car made better progress than the accompanying rear-wheel-drive trucks. Despite this, after a detailed inspection a police colonel submitted a recommendation to have the car converted to pure rear-wheel drive: the numerous components of the all-wheel drive system made it complicated and time-consuming to maintain and repair. This conversion apparently did subsequently take place, but precise details have not survived. There are no records on how the car was used during the First World War. Thereafter, and following the end of German colonialism, all trace of the ‘Dernburg’ was lost – its fate remains unknown. Paul Ritter, its driver and mechanic, returned to Marienfelde in 1919 where he once more found employment with Daimler-Motoren-Gesellschaft.
link to source: media.mercedes-benz.com