Early Development of the Rotary Engine
In 1951, the paths of two groups of engineers crossed for the first time: The NSU research department under the stewardship of Dr. Walter Freode and the Lindau Technical Development Agency (Lindau TDE) led by Felix Wankel first came together to solve very different tasks. However, the revolutionary result of their relationship would come as a surprise. Felix Wankel had already been working on the idea of a thermodynamic rotary engine since 1925. In doing so, he had run through many different options and forms in both theory and practice. The brilliant idea of a piston in a triangular form, a design which still prevails today, came to him spontaneously on 13th April 1954.
Wankel recognised that a certain overlap of two rotary movements produced a geometric shape in the form of a closed curve – a trochoid. This meant it was possible to conceive of an engine with a casing rotating around itself and a triangular body likewise rotating inside it – a curvilinear triangle. He discovered that, if the sealing elements were arranged correctly in this engine, this produced three chambers which in the circular movement alternately increase and reduce their volume. This provided the basic prerequisite for operation according to the four-stroke principle known from the reciprocating piston engine.
The most fascinating finding was that a four-stroke engine operating in this form could be operated, similar to that of a two-stroke engine, without any valve mechanisms and only via adjustable openings. The ground-breaking rotary engine principle was born.
It was necessary to prove that this theory could be implemented in practice. With the support of Prof. Baier from Stuttgart University of Applied Sciences, the circular shape enveloping the piston housing was defined mathematically as a “two-lobed epitrochoid”, and thus the basis for constructing a special grinding machine for the manufacture of the engine was created. The fact that the path being followed was confirmed to be correct, they began to implement models using rotary piston pumps and rotary compressors. One of the first practical applications was a supercharger operating with this system for the record two-stroke engine of the breaking Baumm II car.
However, the end result of all these efforts was the rotary piston test engine DKM 54, which was started for the first time on 1st February 1957 on a test stand at the NSU research department in Neckarsulm, but only for a short time. Once the alcohol-air mixture had been adjusted and the engine was started again, it began to turn smoothly in the truest sense of the word.
ENGINE: DKM 54
DISPLACEMENT: 125 cc Single Rotor
POWER: 27 hp @ 17,000 rpm
While Felix Wankel worked on optimising the cooling of his rotary piston engine in his technical development agency in Lindau, the NSU engineer Hanns Dieter Paschke, together with his department manager Dr. Walter Froede, started to think about the design in a completely new way. Although the rotary piston engine confirmed that the Wankel principle was feasible, the rotary piston engine was still too impractical for regular use.
Paschke therefore set about simplyfying the engine. Whereas with the rotary piston engine of the DKM 54 the piston (internal rotor) and the housing (external rotor) rotated independently around their own axis, the external rotor was then shut down. Thanks to the kinematic reversal of the principle, both rotary movements are combined on one eccentric shaft: The piston rotating about its path on the eccentric circles, and the revolutions of the eccentric shaft now fixed by a synchronised tooth system. For this purpose, the inner gearing is arrange on one side within the piston and this shifts on the fixed pinion of the shaft which is connected to the engine housing.
Work was conducted at NSU under strict secrecy. Felix Wankel was not to know anything about this work as the feeling was that he would not have approved, but Dr. Freode and his team were certain that an engine which was ultimately suitable for standard use in production could only be obtained through the kinematic reversal of the DKM 54 engine into what is now know as the Wankel Engine.
When Felix Wankel found out about this, he was furious about the new engine: “You have turned my throughbred into a plough horse.” The NSU chairman chairman Dr. von Heydekampf replied: “If only we actually had a plough horse!” A few issues with the new engine were already coming to light and so the tests of the DKM 54 were halted in 1958 and a new KKM 57 Wankel rotary engine was started up for the first time on 7th July 1958. KKM 57 was a 125cc Single Rotor engine producing 25 hp @ 11,000 rpm.