Mazda has a long history with rotary engines, going back to the Cosmo Sport and R100 of the late 1960s. With the recently announced demise of the RX-8 — the last rotary-engined model still in production — we look back at the origins of the Wankel engine and the history of the early Mazda rotary engine cars: the Mazda Cosmo Sport 110S, Familia Rotary (Mazda R100), and Luce Rotary Coupé (R130).
FROM CORK TO CARS: THE DAWN OF MAZDA
The company we now know as Mazda dates back to the January 1920 formation of Toyo Cork Kogyo Co. Ltd. (roughly, “Oriental Cork Industrial Company”) in the Japanese city of Hiroshima. The company’s initial business, the manufacture of synthetic cork products, soon fell on hard times, and in early 1921, its creditors appointed a new president, 45-year-old Jujiro Matsuda, a fisherman’s son and one-time blacksmith’s apprentice who had previously founded his own firearms company, Matsuda Works.
Matsuda took Toyo Cork Kogyo in new directions, including the manufacture of machine tools and a brief stab at building motorcycles. By 1927, the cork business had been abandoned, and the company’s name became simply Toyo Kogyo Co. Ltd.
In 1931, Toyo Kogyo introduced its first successful motor vehicle: the Mazda-GO DA Type truck, a three-wheeled, cargo-carrying motorcycle powered by a 500 cc (30 cu. in.) engine. The “Mazda” trademark, also used by General Electric for a brand of light bulbs, was selected primarily as an alternative transliteration of “Matsuda,” but it also meant “wisdom” in the ancient Avestan language of the Zoroastrian religion, most commonly associated with the supreme Zoroastrian deity, Ahura Mazda (Lord of Wisdom).
Initially distributed by Mitsubishi, the little Mazda three-wheeler sold well both before and after World War II, spawning several follow-on models and eventually the company’s first four-wheeled truck, launched in 1950. While Jujiro Matsuda had contemplated building automobiles around 1940, the war and subsequent reconstruction tabled those plans and Toyo Kogyo did not offer its first passenger vehicle until 1960.
Like many early Japanese automobiles, the initial Mazda R360 Coupe was a tiny kei car powered by an air-cooled V-twin engine, not vastly different from the motorcycle-engined European “bubble cars” of the time. Nonetheless, the R360 and the subsequent four-seat Mazda Carol, introduced in 1962, were quite successful in the growing Japanese market, briefly making Mazda Japan’s best-selling automotive marque.
Despite that success, Toyo Kogyo faced a more serious long-term threat to its existence. While the Japanese economy was expanding rapidly, the domestic auto industry was still quite small and very vulnerable. With considerable diplomatic pressure to relax import restrictions, Japan’s Ministry of International Trade and Industry (MITI) was contemplating drastic measures to protect native industry from a potential flood of foreign-made cars. One rumored possibility was a consolidation of domestic automakers into as few as three or four major conglomerates, an alarming prospect to smaller companies like Toyo Kogyo, which under such a plan would either disappear or be absorbed into larger automakers like Nissan or Toyota.
Jujiro Matsuda’s son Tsuneji, who had succeeded his father as president in 1951, decided that the only way for Toyo Kogyo to survive as an independent company was to offer products or technology that rivals could not match. Cars like the R360 and Carol were competent efforts, but they were fairly conventional. For the company to have a future, Mazda needed something unique.
WANKEL DREAMS: THE BIRTH OF THE ROTARY ENGINE
Matsuda found his answer two continents away, at NSU-Motorenwerke in Neckarsulm, Germany, which had recently announced a novel new rotary engine co-developed by NSU and independent engineer Felix Heinrich Wankel.
Although Felix Wankel’s name is still closely linked with the rotary engine, it was not a new idea even when Wankel first started working on it in the 1920s. Plans and patents for rotary steam engines had been developed as far back as 1769, although it’s unclear if they were ever built or would have worked if they had been built. Wankel’s own interest in rotary internal combustion engines had begun when he was only 17 years old, stemming from a dream he once had about a car powered by an engine combining the best attributes of piston engines and turbines. He patented his first rotary engine in 1934 while pursuing a related idea, rotary valves for piston engines. Wankel was subsequently commissioned by the German air ministry to apply the latter concept to aircraft engines, work that led to his arrest and a brief imprisonment after the war. He was released in 1946 and eventually resumed his work at a new research lab in the Bavarian city of Lindau.
In 1951, Wankel signed a consulting agreement with NSU to develop rotary valves for motorcycle engines, later followed by a rotary supercharger. (NSU had made automobiles before the war, but sold its auto business to Fiat in 1929 and did not return to passenger car production until 1957.) However, Wankel remained eager to develop a true rotary engine and lobbied strenuously for NSU to underwrite the project. At first, the NSU board was not overly enthusiastic, but by 1954 Wankel had persuaded company management to share the development costs and any patents related to the new engine.
The engine that we now think of as the Wankel rotary was actually a substantial departure from Wankel’s initial early-fifties concept, the Drehkohlbenmotor (DKM, rotary-piston engine). Developed mostly in Lindau by Wankel and his research partner, Ernest Höppner, the DKM featured a trochoidal (triangular) inner rotor with a spark plug set into one face. Both the inner rotor and the rotor housing (sometimes described as an outer rotor) spun around a common stationary center shaft with the combustion process taking place between the two rotating bodies.
DKM prototypes, which first ran in 1957, had excellent volumetric efficiency — particularly considering that the intake charge had to be routed through the center shaft and inner rotor — and could sustain very high speeds with almost no vibration. From a practical standpoint, however, the DKM left much to be desired. Low-speed performance was poor and high rotational inertia made the engine reluctant to change speeds, problematic for anything other than stationary applications. Furthermore, the transmission or output shaft had to be geared to the outer rotor/rotor housing, which was inconvenient from a packaging standpoint. Changing spark plugs required tearing down the entire engine.
Recognizing those problems, NSU research chief Walter Fröde pushed for an alternative design, the Kreiskolbenmotor (KKM, circuit piston engine), which first ran in mid-1958. In Fröde’s KKM design, a trochoidal inner rotor drove the output shaft via cycloidal gears, causing the rotor to trace an epitrochoidal path (a shape often compared to a peanut or a cocoon) along the inner surface of the rotor housing (see the sidebar on the next page), which unlike in the DKM remained stationary. This approach sacrificed some of the DKM’s smoothness and rev potential as well as posing certain challenges for cooling, but offered much better low-speed behavior and was vastly easier to install and maintain. Wankel was unhappy with the KKM, considering it a cheapening of his concept, but the practical advantages were hard to ignore. The NSU board made it clear that the cash-strapped company could not afford two different rotary designs, so Fröde eventually persuaded Wankel to abandon the DKM.
Even so, the rotary project was a big gamble for NSU, and the Neckarsulm firm lacked the resources to fully develop or exploit the new engine on its own. With prototypes running on test stands, NSU started looking for partners and licensees to share the work and the cost. The first was the American aviation company Curtiss-Wright, which in October 1958 paid a reported $2.1 million (plus a 5% per-engine royalty) for exclusive, sublicensable U.S. rights. Over the next few years, NSU would receive more than 100 other license requests covering everything from lawnmower engines to heavy-duty diesel applications.
When Tsuneji Matsuda heard about the rotary engine in late 1959, he concluded that it was exactly what Toyo Kogyo needed. The rotary was mechanically elegant, had great potential, and was radically different from anything else on the road. Matsuda made initial overtures in early 1960 and visited Neckarsulm with a group of engineers that October to see NSU’s development engines and negotiate the licensing agreement. MITI approved the deal in mid-1961. The reported license fee was ¥280 million (about $780,000 at the contemporary exchange rate).
The agreement gave Toyo Kogyo the right to use and sell the rotary engine in Japan and Asia. All they had to do now was make it work.