Rotary Engine

History of Rotary

Engineering History
The Birth of the Rotary Engine
In Search of the Ideal Engine

In November 1959, NSU officially announced the completion of the Wankel rotary engine. Approximately 100 companies throughout the world scrambled to propose plans for technical tie-ups.

Mazda's president, Tsuneji Matsuda, immediately recognized the great potential of the rotary engine, and personally began direct negotiations with NSU. Those negotiations resulted in the formal signing of a contract in July 1961, with the approval of the Japanese government. The first technical study group was immediately dispatched to NSU, while an in-house development committee was organized at Mazda. The technical study group obtained a prototype of an NSU-built 400cc single-rotor rotary engine and related drawings, and learned of the "chatter mark" problem. This was a phenomenon where wavy traces of abnormal wear appeared on the rotor housing, causing the durability of the housing to significantly deteriorate, and was the most critical barrier to full development. It remained a problem even inside NSU.

In November 1961, while it was testing the NSU-built rotary engine, Mazda produced its own prototype, an engine independently designed in-house. Both engines, however, were afflicted by chatter marks. Practical application of the rotary engine was not possible without first solving this problem.


Nail Marks of the Devil

In April 1963, in an effort to solve the chatter mark problem and enable the future commercial application of the rotary engine, Mazda formed its RE (Rotary Engine) Research Department. Under Mr. Kenichi Yamamoto, chief of the department, 47 engineers in four sections--investigation, design, testing, and material-research--began working tirelessly on the long road to achieving mass production of the engine. The most critical engineering obstacle they faced was how to eliminate the chatter marks, which they dubbed “nail marks of the Devil.” The RE Research Division discovered that chatter marks were made when the apex seal, which filled the gap between the housing and the rotor, vibrated at its inherent natural frequency.

Chatter Marks
Chatter Marks
The durability of early rotary engines was severely affected by these wavy traces of abnormal wear on the inside surface of the trochoid housing.

To eliminate this phenomenon, a cross-hollow seal was developed by drilling small holes inside the metallic apex seal. This greatly improved the durability of the prototype engine, enabling it to complete 300 hours of continuous high-speed operation. In the end however, this technique was not adopted in the mass-produced rotary engines, but it did serve to promote further research into the materials and structure of the apex seal and led to great enhancements in the durability of the housing.

Also in the initial stage of rotary engine development, engineers were faced with the further problem of engine oil leaking into the combustion chamber, causing excessive oil consumption. The team identified the oil seal as the cause of the problem, and developed an innovative Mazda-unique oil seal in conjunction with Nippon Piston Ring Co. and Nippon Oil Seal Co.

In overcoming such challenging technical issues, Mazda was steadily moving forward with its rotary engine development project, getting closer to commercial viability.

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Related information

As the President of Mazda, Tuneji Matsuda took the initiative in proposing a technical cooperation plan with NSU for the development of the rotary engine and obtained the approval.

Kenichi Yamamoto

Kenichi Yamamoto

As the chief of the RE research department, he played a key role in developing Mazda's rotary engine. Later served as President and then Chairman of the company.

KKM 400 Rotary Engine

KKM 400 Rotary Engine
The NUS-built single-rotor prototype engine sent to Hiroshima from Germany with its technical drawings. This had a chamber volume of 400cc.

How a Rotary Engine Works

Watch an easy-to-understand animated explanation of how a rotary engine works.