RX-Rated: Mazda’s Early Rotary Cars, Part 1

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).
1971 Mazda R100 coupe badge

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” trade name, 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.

1964 Mazda R360 Coupe front 3q copyright 2010 Rex Gray (CC BY 2.0 Generic) modified by Aaron Seversno
A 1964 example of the Mazda R360 coupe, Toyo Kogyo’s first passenger car. Launched in 1960, it was powered by a 356 cc (22 cu. in.) air-cooled two-cylinder engine with 16 hp (12 kW); since the R360 weighed less than 900 lb (about 400 kg), that was enough for a top speed of around 55 mph (90 km/h). At introduction, the R360 cost only ¥300,000, equivalent to about $835. A four-cylinder model, the Mazda Carol, followed in 1962. The R360 was discontinued in 1966, but the Carol survived through 1972. (Photo: “1964 Mazda R360 Coupe” © 2010 Rex Gray; resized and modified 2011 by Aaron Severson and used under a Creative Commons Attribution 2.0 Generic license with modifications offered under the same license)

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.

Felix Wankel 1950s copyright Mazda
Felix Wankel, circa the late 1950s. (Photo circa 1958, copyright and courtesy Mazda)

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.

1957 Drehkolbenmotor DKM54 stand copyright 2005 Ralf Pfeifer at German Wikipedia CC BY-SA 3.0 Unported
Felix Wankel’s first running prototype Drehkohlbenmotor, the DKM 54, photographed at the Deutsches Museum in Bonn in 2005. (Photo: “DrehkolbenmotorDKM54” © 2005 Ralf Pfeifer at German Wikipedia; resized 2011 and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

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.

27 Comments

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  1. I’ve always loved Mazda’s rotary cars. Fantastic article, and I can’t wait for part 2…

  2. Great story looking forward to part 2. A friend in Tasmania had several of those bertone Luces nice cars the later models had the 1800 Capella engine.

  3. Thanks for the Mazda rotary article. I’m looking forward to reading Part 2. Despite growing up around Mazda rotary-powered cars, I learned quite a bit!

  4. It’s a real shame that no one can seem to lick the engine’s fuel and oil consumption problems. I have heard some discussion of Mazda using rotaries in hybrids, which makes some sense to me. Rotaries are so small and, on paper at least, elegantly designed.

    Man, that Luce coupe is a looker.

    1. I don’t know about hybrids, but Mazda has done quite a bit of development on a hydrogen-fueled rotary, which has been offered on a limited basis for fleet sales in some markets.

      If the next-generation 16X engine materializes, Mazda is hoping to reduce fuel consumption substantially, in part by adopting direct injection. Still, since piston engines keep improving in that regard, as well, I don’t know that the rotary will ever match the reciprocating engine in specific fuel consumption. Some things can be mitigated (like wall quench), but other factors, like the combustion chamber surface area to volume ratio, are sort of the nature of the beast.

      The Luce R130 is indeed a very nice-looking car. I’d never seen one before I started researching this story.

  5. Very interesting article, well, as usual, Aaron!
    The topic was somewhat forgotten in France after Citroën heavily invested in the technology, eventually failed to make it work and had to drop the project in the early 70’s. They had been so serious about it that the models developed in the late 60’s, the GS and the XM, were designed for a rotary. They had to hastily develop a reciprocating engine for the GS and make it fit in the engine bay that was not large enough.
    The XM eventually was painfully fitted with a Peugeot engine.
    Anyway Citroën was never able to design a good engine. This huge investment and its failure played an important role in the demise of the company.

    Nick

    1. “They had been so serious about it that the models developed in the late 60’s, the GS and the XM, were designed for a rotary.”
      You mean the SM, don’t you?

      1. I believe Nicolas was probably referring to the CX, which replaced the Citroën DS in 1974. I’ve never heard anything about the SM being intended for rotary power — of course the production cars had the Maserati V6 — but I think the CX was. The XM was the CX’s eventual successor, introduced in the late eighties.

  6. Right Aaron, my pen slipped, it was the CX.
    The XM was its successor.
    The SM, stangely enough, was fitted with the (in)famous Maserati V6 even though Citroën had such a faith in the future of the rotary as the ultimate replacement of the reciprocating.

    Nick

    1. Timing may have had something to do with it. Citroën didn’t build the first M35 single-rotor cars until the fall of 1969, and as I understand it, they were essentially evaluation models, not yet intended for large-scale production. The BiRotor wasn’t introduced until 1974, about four years after the SM debuted. Even if Citroën were keen to give the SM rotary power, it probably wouldn’t have been ready until a few years after launch, even in a best-case scenario.

      If things had worked out differently, I imagine Citroën might have added a rotary engine to the SM later, perhaps in a second-generation version for the mid-seventies. Of course, even if the Comotor engines had been more successful, the SM was not, and might have been dropped without ever getting a rotary engine.

  7. For them the rotary was the future type of engine for all applications, just as well as they were persuaded they had a market for the SM.
    With NSU, Mazda and others working on it it’s understandable.
    Your article is very interesting by showing how Mazda made a success of it, or at least could partly make a living with it, well… that’s a success, isn’t it?
    Strangely enough it didn’t catch on as an aviation engine either.
    Nick

  8. [quote=Administrator] Citroën didn’t build the first M35 single-rotor cars until the fall of 1969, and as I understand it, they were essentially evaluation models, not yet intended for large-scale production. The BiRotor wasn’t introduced until 1974, about four years after the SM debuted.[/quote]
    Starting in 69 a limited number M35, and in 73 GS Birotor, were sold to selected, faithful (and masochist) clients but the engine proved such a burden to maintain that Citroën offered to buy them back and scraped them. A few people only turned down the offer. The maintenance contracts were canceled for them. The few models still in existence are now very expensive collectors’ items, the day dream of all the GS enthusiasts.
    So there was actually a future for the rotary! ;-) As usual the car that nobody wanted became the car that nobody can afford.

    Nick

    1. The source I was looking at (John Hege’s [i]The Wankel Rotary Engine: A History[/i]) suggests that Citroën had basically intended to buy back the early evaluation engines from the outset, which would make a lot of sense.

      I don’t know about France, but in the U.S., automakers are legally obligated to provide parts support for production models for a specific period of time, typically 15 years — obviously not an appealing prospect for cars or engines that don’t end up in mass production! For that and other reasons, some automakers have tended to offer such evaluation vehicles only as a closed-end lease or other type of loan-out, with no option to actually purchase and keep the vehicle at the end; I assume that not actually selling it avoids triggering certain legal requirements.

  9. The Europeans have basically the same obligations as the Americans. As far as I understood, the deal was under specific conditions and since Citroën offered to buy them back it could cancel any support for those who rejecter the offer. It’s stupid it didn’t keep one example for history.

    Mazda is the only one who succeeded with a rotary over the years while all the others flopped.
    Well done!
    Nick

  10. This is an interesting article as usual, I’m waiting for the second part. While you’re at it, how about an article covering GM’s attempt to build a rotary engine?

    1. I thought about it, but in researching this article, I’m finding that detailed information about its development seems to be surprisingly scarce. While the development of the NSU, Mazda, and Curtiss-Wright engines is pretty well-documented, GM played it very close to the vest. To really do it justice would probably require talking to some of the engineers who worked on it, assuming that the people involved are still living, and willing (and able) to talk about the program.

  11. No need to mourn it’s passing. A technological dead end. I don’t miss the
    ffffttttt exhaust “note” of them at all.
    Used to be a few about Brisbane, Delighted to see and hear that rust and enlightenment of the owners has made them almost extinct.

    Good riddence. So it could rev to 5 digits.
    BFD.

  12. Wow, FANTASTIC article! Thanks for the great piece on Mazda, the detail and depths you go to are above and beyond. One of the best history-of-automaker stories that I’ve read. Thanks again!

  13. Another great article Aaron. Really appreciating your narrative drive and level of scholarship. I’m starting to believe the R100/1200 body was designed by Bertone as well, but can’t verify. Do you know of any text that addresses the connections between the Italian design houses and the Japanese manufacturers in depth?

    1. I so far haven’t found anything to suggest one way or another whether the first-generation Familia was done by Bertone, although it’s certainly plausible given that Bertone did the first Luce and the Luce Rotary Coupé in that period. Even if Stilo Bertone didn’t do the Familia or the first Capella, those designs have a definite Italian flavor, much more so than subsequent products of Toyo Kogyo’s in-house design studio, which feel more typically mid-seventies Japanese.

  14. I really like that little sidebar referring how to calculate the Wankel’s full displacement. I know Japan has different regulations than the U.S. and that Mazda had no choice to only count one chamber for each rotor (Geometric Displacement) due to extra taxes being placed on “bigger” cars. Either way, I really hope Mazda brings their Wankel rotaries back to the streets, because that awesome RX-Vision concept needs to be on the roads

  15. In retrospect could the prospects of the Rotary have been slightly improved to a certain extent had Mazda and not Citroen established the Comobil later Comotor joint-ventures with NSU, where the development of the Rotary follows a more developed Mazda like trajectory instead of the engine being prematurely released as was the case with NSU and Citroen?

    Would that have been enough had it been feasible to largely butterfly away the poor reputation and resolve the issues of the early Rotary engines or would more changes have been required? Taking into consideration of course the current disadvantages of the Rotary would still remain.

    1. This is one of those “could / would /should” questions. The “could” part is straightforward, at least technologically speaking; Mazda obviously managed to keep the rotary at least reasonably viable for many years, so there’s no technical reason the fruits of their efforts couldn’t have been shared across a broader consortium.

      The “would” and “should” parts are more complicated. NSU-Wankel patent licensing agreements generally included technology-sharing provisions because NSU did not have deep pockets and figured that pooling research data would be the best way to advance the art. (Part of the reason GM’s patent license was so expensive is that GM didn’t want to participate.) Toyo Kogyo participated in that and probably contributed quite a bit to it. However, the way that knowledge was applied ended up being dictated by other factors, including a maze of different licensing agreements (like the one with Curtiss-Wright that affected distribution in North America), the concessions NSU minority stockholders wrested during the Audi merger, and the fact that the Comobil/Comotor project contributed to Citroën’s financial over-extension and eventual bankruptcy.

      Would NSU stockholders have agreed to set up such a consortium or joint venture with Toyo Kogyo? Possibly, and in that area, the progress Mazda had made with the technology might have been attractive. Would Volkswagen have been amenable to it after the NSU-Audi merger? Harder to say; I don’t imagine that Volkswagen or Audi were terribly keen on Comotor given the NSU shareholder concessions, and Toyo Kogyo being involved in that venture rather than Citroën (or succeeding Citroën) would not have changed that part of the equation. The minority shareholder deal ended up signing away most of the opportunity to profit from the rotary, and Volkswagen still wouldn’t have been in a position to use the rotary in its own products. (I don’t think Toyo Kogyo would have been in a position (financial or political) to acquire NSU instead of Volkswagen.) The main point of change in that scenario is that Toyo Kogyo by then had sunk enough money into development that they were more reluctant to simply shelve it.

      Should they have? It depends on a lot of things. If Toyo Kogyo had stepped in AFTER Citroën had been forced to bow out, the venture would have had to rebrand and might still have had a shaky image. There were customers who would have been interesting (AMC, to name one), but Mazda rotary combustion engines of the early seventies were still not without flaw, and the issues might have caused their licensees to jump ship early. (Toyo Kogyo commitment to the rotary had a lot to do with pride and the sunk-cost fallacy, to be honest.) Also, the OPEC embargo would still have really pressed the rotary’s limitations in terms of fuel consumption, which would have still hurt the project’s commercial prospects.

      So, an interesting idea, but I tend to see it coming to a similar end.

      1. Do not envision a joint-venture between NSU and Mazda in place of NSU and Citroen significantly changing things once Volkswagen acquires NSU and merges it with DKW/Auto Union to form Audi, what with the fuel crisis hurting the rotary engine’s projects in Europe. That said the NSU Ro80’s issues would have been largely butterflied away for one thing, though not sure if it would be enough for Volkswagen to actually consider a rotary model for say the 914 (as was experimented in real-life) if not a small mid-engined sportscar or some other vehicle (.

        For Citroen there is one less contributor to its financial over-extension and eventual bankruptcy, leaving only one or few more elements (e.g. Project F, possibly acquiring Maserati for V6, SM instead of DS Sport, etc) to be remedied on its end without being involved in the Comobil/Comotor project. What Citroen goes from hereon is another matter, in the absence of the French government forcing Peugeot to acquire Citroen perhaps Citroen ends up increasingly entangled with Fiat or collaborates with one and more carmakers on a few joint-ventures outside of Fiat (e.g. Alfa Romeo? Subaru? both? etc).

        Essentially the rotary engine in this scenario would be better regarded compared to real-life thanks to Mazda’s early tie up with NSU and a thorough development programme (instead of being prematurely released), yet ultimately undermined by the fuel crisis and only really considered worthwhile for sportscars.

        1. The issue pertaining to the NSU-Auto Union merger (which is explained in more detail in the Ro80 article) is that Volkswagen ended up signing away the lion’s share of Wankel-related profits and agreeing that if it used the rotary in its own products, it would have to pay license fees like any outside customer. In the short term, that was a big win for NSU minority shareholders, but it probably contributed a lot to the eventual stagnation of rotary development outside Toyo Kogyo/Mazda. On the other hand, NSU’s survival WITHOUT a merger would have been very tenuous because they had also overextended their resources with the Ro80 and what became the Volkswagen K70. Whether Toyo Kogyo would or could have afforded a merger with NSU that would have obviated the need for the Volkswagen deal I don’t know; it would have been a politically complex situation, to say the least.

          NSU was undoubtedly aware of everything Toyo Kogyo had been doing regarding rotary development, which to my understanding was a condition of the original license agreement. (I assume NSU would still have had to formally license technology subject to Toyo Kogyo patents, although I don’t think that would have been an insurmountable obstacle.) However, the problem they both faced is that each was exploring different solutions to the challenges involved (like the apex seal issue), and it wasn’t yet apparent what would work best. Toyo Kogyo didn’t attempt anything quite as daring as the NSU floating seal design (which was a brilliant idea undermined by inadequate development testing), but the differences between the earliest 12A twin-dizzy engines and the better-developed 13B found in the first-generation RX-7 are pretty substantial. It’s not that Toyo Kogyo was smarter or luckier than NSU in this regard; it’s that they kept working on it and refining their approach to factors like sealing and porting.

          However, the upshot I assume you’re getting at is that an alliance between NSU and Toyo Kogyo might have resulted in a more lasting commitment to developing the rotary engine as a commercial prospect, with a Comobil/Comotor-style entity offering engines to other companies that were interested in the technology, but either couldn’t afford or didn’t want to spend the money on developing their own. The actual reason that didn’t happen was probably mostly that Volkswagen had very limited financial incentive to bother and Citroën, as mentioned, ran out of money. If Volkswagen were not in the picture (or the settlement with the minority stockholders had turned out differently), NSU survived on its own, and Toyo Kogyo took Citroën’s place as development partner, it might be plausible.

          One other fly in the ointment with that scenario, though, is European hostility toward Japanese automakers. As much as the emergence of Japan as a major player on the automotive scene aroused horrendous racism and nationalistic furor in the U.S., that hasn’t significantly dissuaded Americans from buying Japanese cars, to the point that domestic automakers have more or less abandoned many segments of the market to the Japanese and Koreans. European markets have not been nearly so amenable, and even products Japanese automakers have designed specifically for Continental or British tastes have often been commercial duds. Applying that chauvinism to the early seventies, it’s also not hard to envision a scenario where Toyo Kogyo partnership in a Comotor-type JV ends up leading European punters and pundits deciding that rotary engines are too Japanese, which combined with the pressures of the OPEC embargo might also have been a death knell.

          1. Volkswagen could have attempted to use the rotary in more niche segments like Mazda did with front-engined sportscars though mid-engined in Volkswagen’s case, otherwise Volkswagen could be a passive beneficiary at best upon buying NSU.

          2. As it says in the Ro80 article, there was a lot of enthusiasm within Audi-NSU for the planned Ro80 successor, including some fairly serious talk of installing its 1.5-liter KKM 871/EA871 engine in the Audi C2. However, the minority shareholder settlement would have made using that or other Wankel engines in Volkswagen models fairly costly, which I think was a big part of why the whole plan ultimately didn’t go anywhere.

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