Electric drive and wheel hub motors: First buses back in 1899
When commercial vehicle development chief A. H. Müller-Berner and engineer P. Strifler presented the OE 302 diesel-electric hybrid urban bus in Automobiltechnische Zeitschrift in 1970 – marking the beginning of the development of alternative drive systems at Daimler-Benz – in their introduction they recalled a forerunner from the year 1899. The bus, lettered “Kaiser Hotel” and strongly reminiscent of a horse-drawn coach, came from Motorfahrzeug- and Motorenfabrik Berlin-Marienfelde, which merged with Daimler-Motoren-Gesellschaft (DMG) in 1902. A DMG sales brochure of 1900 describes the bus as follows:
“Our electric hotel bus shown above is the carriage par excellence for any modern hotel! Its advantages include noiseless and odorless travel, excellent steering and control, and, in addition, the quality that it is always ready to go. During short stops, for instance while waiting at the train station or in front of the hotel, the driver can leave it entirely unsupervised, perfectly safely, since the motor is stopped and, by withdrawing a key from the emergency stop switch, the driver makes the braked vehicle inoperable for any unauthorized person who is not in possession of the key.”
“Having now had the electric hotel bus in operation for one year at our hotel, I absolutely must confirm to you that the bus has always functioned excellently and provided smooth service,” the director of Hotel Kaiser on Friedrichstraße stated, and Allgemeine Berliner Omnibus-Actien-Gesellschaft agreed: “In response to your inquiry of the 20th of this month, we can tell you that so far the buses with electric drive system for 17 and 18 passengers put into operation by our transportation service have run well, as far as we can judge.” And there were several such electric buses plying busy Friedrichstraße in those days, as an enclosed photograph shows. Under favorable conditions they attained a range of 40 kilometers and a top speed of 18 km/h and could be had for a price of about 12,500 marks.
Wheel hub motors for hybrid and trolley operation
At the same time, Ferdinand Porsche, then employed at Hof-Wagen- and Automobilfabrik Jacob Lohner in Vienna, invented the wheel hub motor. When the young engineer went to Austro-Daimler in 1905, DMG seized upon the patent and produced the electric motors, which were fitted into the front wheels, in large numbers so that the system soon simply was called “Mercedes Electrique” or “Elektro-Daimler”.
At Austro-Daimler, Porsche also sought to bring his invention together with the core competence of the gasoline engine manufacturer by replacing the heavy lead storage batteries of the electric vehicle by a gasoline engine and generator which produced the electricity for the wheel hub motors: the hybrid drive, called Daimler-Mixte, was born. The bigger range compared with the storage battery, but above all the vehicles’ problem-free, permanent readiness for use, made the Mixte drive system an attractive solution for fire departments which until then had turned out to the scene of a fire at worst with horse and cart and bicycles, at best with electric and steam-powered automobiles. The big professional fire departments in Berlin and Hamburg soon put Mixte vehicles into service. Of course, the twin drive was a little more expensive for the customer than pure electric or gasoline drive.
But the wheel hub motors could be used for trolleybuses as well. Significant progress had been achieved in that area since the beginning of the century. Engineer Carl Stoll further developed the Lombard-Gérin system which won a gold medal at the 1900 Paris world exposition. In 1902 he commenced trial operation on the 5.2 kilometer “Haidebahn” between the Arsenal industrial estate and Klotzsche near Dresden. The bus pulled a four-wheeled contact carriage, the trolley, behind it on an overhead cable. During the one year of scheduled operation from March 24, 1903, to March 19, 1904, the Haidebahn line actually carried 133,000 passengers. The Stoll System thus had demonstrated its practical suitability.
After Porsche joined the company, Austro-Daimler was soon also offering trolleybuses according to the “Mercedes-Electrique-Stoll System.” “An up-to-date, first rate, cheap means of transportation!” a 1909 brochure published by DMG Berlin-Marienfelde states: “Is a full-fledged replacement for an electric streetcar for smaller enterprises. Costs only a third of the streetcar and has lower operating expenses.” Depending on the length of the route and the number of vehicles and their equipment, a transportation service had to reckon with investment costs between 50,000 and 200,000 marks.
The first town, Gmünd in Lower Austria, took up operation in July 1907 on a 3.3 kilometer line between rail station and city center. The two 18-seat vehicles still had the wheel hub motors in the front wheels. Later Daimler switched to rear-wheel drive. In 1909, 25 trolleybuses were already operating on six lines in Greater Vienna, in Pressburg (Hungary then, today’s Bratislava in Slovakia) and in Budweis (České Budejovice). Judenburg, in the Styria region, where the bus had to negotiate a 15 percent incline, followed in 1910. With a top speed of around 25 km/h even uphill, the trolleybuses were clearly superior to gasoline-engined vehicles in those days.
A trolleybus line took up service in Germany for the first time on January 16, 1911, in Heilbronn. The 5.5 kilometer distance to the blue-collar suburb Böckingen presented unusual challenges to the construction engineers of Ludwig Stoll’s project office. There was a level crossing with a railway line, and in another place the overhead cable had to be routed under a 3.77 meter high railway bridge. By 1912 further lines had been started up in Fribourg in Switzerland, in Berlin-Steglitz, and finally even in Paris. At that point, 40 vehicles were operating on eleven lines with a total length of around 50 kilometers, and all were still providing reliable service after almost two million vehicle-kilometers.
O 6000 and O 10000: Trolleybuses of the 1930s
Trolleybus operation was discontinued during the First World War, and after the war there were no funds for new investment at first. Daimler-Benz first presented a trolleybus again in 1936 at the International Automobile and Motorcycle Show (IAMA) in Berlin. Since 1930 trolleybuses had begun to see service again in Germany, but the concept really owed its renewed breakthrough to the policy of the National Socialists, who wanted to make themselves independent of imported oil.
The 9.375 meter long 32-seater, developed jointly by Daimler-Benz and Brown, Boveri & Cie. (BBC), appeared astonishingly up-to-date: It was a square-faced, all-steel, cab-over-engine vehicle built on a low-frame chassis with a floor level of 70 centimeters above the ground and with wide, double folding doors at the front and in the middle. The engine output was 73.5 horsepower; the top speed was 40 km/h. But what made it special was that the contact-wire bus, as it was called then, needed no gearshift.
“We’ve trodden completely new paths with the electric controls. Starting from the realization that the driver of such a vehicle must direct all his attention to the road, the REGULATION of the motor has been AUTOMATED, i.e., the usual gradual flooring of, or repeated stepping on, the accelerator was eliminated. In this new design the ACCELERATOR ONLY HAS TO BE STEPPED ON ONCE to start off and accelerate; the further shifting of the drum of the drum starter from step to step is performed automatically by a rotary magnet. The rate of progress depends on the supply of power from the motor: the speed adapts to the topographic conditions and is slower on gradients than in the flat. This avoids excessive OVERLOADING of the motor.”
In 1937 the company then launched a complete series of trolleybuses starting with the O 4000 for 39 passengers. However, of the four models, which now came in rounder shapes, only two were ever produced, the O 6000 and the O 10 000. All in all, though, no more than 26 units were produced, as an internal investigation found in 1952. Actually, another 264 orders were received through 1942, but a decision by the Nazi rulers to take trolleybus production out of the war program brought the further completion of these orders to a halt on March 12, 1943.
Copyright © 2008, Mercedes-Benz-Blog. All rights reserved.