“Its captivating simplicity”, as Lehmbeck and Isendahl described in their 1911 engine bible, prompted German designers to pursue the two-stroke engine. Later, “before which it is not possible to expound expressly enough, when it comes to using the two-stroke engine for automobile operation ... The tests ... have led to negative results and swallowed up sums that are lost forever and the failures have deprived the ground of two-stroke engines for the future."
To state it boldly, German designers in particular cultivated the two-stroke engine for cars in the period before and after World War II and were able to achieve remarkable successes first with reverse scavenging and later with gasoline injection. Herbert Venediger was probably the first two-stroke theorist to play a major role.
After completing his studies and obtaining his doctorate of engineering with a treatise on two-stroke petrol engines, Venediger was looking for experience in industry and the opportunity to conduct further research. In May 1932, in the middle of the Great Depression, he obtained a job as a self-employed engine designer at Zschopauer Motorenwerke, J S. Rasmussen AG (DKW). There he was directly subordinate to the management, who did not assign him as a normal engineer to new designs, but instead let him investigate the question of whether the large-scale production of supercharged double-piston engines, as suggested by the freelancer Arnold Zoller, could be realized , and if so at what cost.
Instead of using double-pistons, or two-stroke engines with supercharging, Venediger recommended converting the series engines from cross-flow scavenging with domed pistons (see above) to the Schnurle dual-flow reversing scavenging with flat pistons. In 1932, Rasmussen subsequently acquired the sole license for the corresponding patents from Adolf Schnurle, who was working for Humboldt Deutz Motoren AG in Cologne at this time.
After the changeover to the reverse scavenging process in 1932/33, the DKW engines were suddenly superior to all competition, not only for motorcycles, but also for the stationary and multipurpose engines, as well as the two-cylinder automobiles of the Reichs and Meisterklasse types. The Special-class and floating-class models with four working and two charging pump cylinders in V-shape, on the other hand, retained cross-flow scavenging (and continued to cause considerable annoyance for customers and the factory).
Zundapp, Triumph, Victoria, Motosacoche and other motorcycle companies quickly became aware of their technical deficit compared to DKW engines. In order not to infringe on the licenses of the Auto Union / DKW, they offered motors with a similar flush system. The Auto Union patent division, to which Venediger was transferred from March 1933, suddenly found himself faced with an unprecedented workload, because now the Schnurle patents had to face the competition to be defended. What had to come happened: The industry experienced sensational court rulings, with a relentless Venediger in the key role. With him as a specialist in two-stroke engine technology and patent law, Auto-Union won all of the proceedings relating to reverse scavenging gas flow. Venediger later admitted, "I have done enough good in this area for the past 15 years (and) don't admit monopoly of exclusivity to be in accordance with time or development, or even necessary." Perhaps he had in mind the trial before the Reichscourt in Leipzig, which at the time followed Venediger's argument and had given Zundapp a fine of millions. Wrongly so, because the Zundapp’s three-flow purging was a real technical advance, which could only be incorporated into the two-stroke engine construction after the Schnurle patents expired in 1960. Among other things, we would like to remind you of the "Dreistromer" racing engines, which were used very successfully by DKW tuning master, Albrecht Wolf Mantzel, and also by Auto-Union itself in DKW racing in the first half of the 1960s.
But back to the 1930s. In addition to the patent litigation that Venediger led until 1938, In June 1935 he took over the management of a new development department for the two-stroke area with an attached test department. In addition to general work such as compound lubrication, thermal stability, improved crankshafts, gasoline injection and reduction in fuel consumption, as well as improvements to products from the current series (7 industrial engines, 5 motorcycles, as well as the Master and Special / Floating classes), new models were also developed there: the motorcycle RT 125 and NZ, plus eight industrial engines and the 900 cc three-cylinder engine for the DKW F9 (then under development and which was originally planned to be launched in 1940). Because of the war the F9 did not go into series production until 1950 as IFA F9 in the GDR and in 1953 as DKW F 91 Special class at the newly founded Auto-Union GmbH in West Germany. Here, the three-cylinder engine was able to hold on in the DKW Munga until 1968, while in East Germany it was installed in the various Wartburg and Barkas models until 1988.
So Auto-Union AG should have been quite satisfied with the work done by Venediger, who was not always easy with people. According to Venediger, he wanted an appointment as a deputy member of the board for the introduction of the reverse scavenging, for the patent litigations he had won, for the establishment of an efficient development and testing department and for the development of the three-cylinder engine. But when he found out at the end of 1939 that he was not even considered (inevitable in the event of war), Venediger announced his termination of his relationship with Auto-Union on January 20, 1940.
From the perspective of that time, and also in retrospect, to sum up, the proportion of two-stroke engines had increased steadily since the 1920s. This development was largely due to the reverse scavenging, which MAN, in particular, implemented for their slowly rotating large diesels and Auto-Union, with its DKW brand in the fast rotating small petrol engines. At Auto-Union, Venediger had set the course for the reverse scavenging.
When Venediger left Auto-Union, Germany was at war. Venediger, who had once been convinced by Hitler, had changed during the 1930s to a fanatical Nazi hater, who was now only concerned with survival, i.e. a "UK" position. He believed that he found such at Mechanische Werke Cottbus GmbH, a branch of the Phanomen-Werke Gustav Hiller AG in Zittau. In January 1940, Venediger occupied the post of Technical Director at MWC, which, as a purely military company, sold the 1-tonne half-track traction vehicle under license Demag, later also as self-propelled guns with Pak and the light armored personnel carrier D7P, for reconnaissance. These years, initially carefree in spite of the war, ended with an accusation against Venediger of sabotage, anti-state attitudes, and damage to war supplies. After the unsuccessful attempt to assassinate Hitler on July 20, 1944, his situation deteriorated further, as did that of his wife, who was also banned by the Gestapo. He wanted to avoid being arrested and condemned by the People's Court under its sadistic and brutal president, Roland Freisler. However, with the help of a friendly SS man, he managed to slip away to the west of Germany.
A new phase of life followed with short-term, maximum two-year employment relationships with changing employers. This was due to the politically and economically chaotic conditions before and after the end of the war in May 1945, but above all to a motorcycle accident in November 1949. While riding an Ardie test machine, the third gear suddenly locked at approx. 80 km/h, and Venediger was catapulted over the handlebars, causing a skull base fracture, bruising, visual impairment, and other consequences of the accident. The professional association classified him initially as being 30% and then 40% fit for work, making it only partially possible for Venediger to take a job for a longer period. He therefore reverted to an expert and consultant role and, with a new sponsor in the background, also acted as a licensor. For example, from 1952 to 1954 Flottmann-Werke GmbH in Herne, which employed Venediger as a consulting engineer, tried to use his industrial property rights on engines with rotary piston valves. From 1955 to 1959 Venediger hired himself as a freelance employee at Durkopp-Werke AG in Bielefeld, which showed interest in reverse scavenging for diesel engines. He granted licenses to an American company in Inglewood, California, for counter-piston two-stroke diesel engines for boats. In fact, these went into series production but because Venediger’s scavenging design was changed without knowledge, the pistons seized after a few hours of operation. The company went bankrupt, but the bottom line was that this US venture (1957-1962) had raised 73,615 marks and 23 pfennigs according to Venediger's meticulous records.
The aftermath of his motorcycle accident in 1949 finally made him 80 percent unable to work in 1963. For the ambitious, strong-willed and energetic Venediger, at that time just around 60 years old, this was an extremely depressing situation.
He switched to philosophy, theology and astrology, successfully invested in securities, and married a second time ,after his first wife's death in 1973. In a book about DKW in which he participated, author Siegfried Rauch recalls the years in which Venediger "made such a decisive contribution to the fact that DKW became a global brand." But the motor press and the companies he had once worked for took no notice of his death in September 1988. His contributions in the ''Automotive Technical Manual", his publications in the ATZ ,and his major work" Evaluation of scavenging in Two-stroke engines", published in 1947 by a Frankfurt publisher, remain valid today in its basic findings.
[a copy can be found online here: https://digital.library.unt.edu/ark:/67531/metadc63504/]
Text: Erik Eckermann
Fotos: AUDI AG, Kurze, Erdmann, Eckermann
I did a driving video some time ago and discussed the early development of the two-stroke motor.
