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NSU Wankel rotary engines and cars

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Introduction / NSU History / NSU Engine development / NSU DKM Engine / NSU KKM Engine / NSU Licensing / NSU Wankel Spider / NSU Ro80 / NSU'S Downfall / More Information


NSU, from Germany, was the original partner that developed production versions of the rotary engine with Dr Felix Wankel. As NSU had several patents on the rotary, all other manufacturers had to pay a license fee to NSU. This is in fact cast into every Mazda rotor housing saying "NSU-WANKEL LICENSE"

Two rotary powered NSU cars were produced, The single rotor NSU Wankel Spyder (which was the first production rotary car in the world) and the twin rotor NSU Ro80 (Mazda beat NSU to be the first production twin rotor engine with the Cosmo Sport, by 3.5 months).
Unfortunately the technology at the time did not match the concept of the Wankel engine and the resulting problems led to the end of NSU as a marque.

A brief history of NSU

NSU started in 1873 making sewing machines before making bicycles ten years later, followed by motorbikes at the turn of the century.

It wasn't until 1892 that it got the name NSU. Motorcycles were first produced in 1901.

The first cars appeared in 1905 and were produced until 1930 when Fiat bought the factory in Heilbronn. Production of bikes and motorbikes continued and Scooters and the well known "NSU Quickly" were manufactured from the early 1950s. In 1955 it was the largest motorcycle manufacturer in the world. Production of two wheeled vehicles ceased in 1965.

1957 saw the return of NSU to the car business with the Prinz 1, a small aircooled rear engined car (583cc 2 cylinder). This was followed by the Prinz 2 and Prinz 3, then the restyled Prinz 4 with a larger 598cc engine. The Sport Prinz was procuced alongside the Prinz 4 with both the 583cc and 598cc engine.

A range of larger 4 cylinder cars were also made based on the same body shape as the Prinz 4. The first was the Prinz 1000 later badged as the NSU 1000 with a 996 cc engine.Two high performance models followed, the TT and the TTS. The TT had a 1085cc then 1177cc engine with twin carburetters. The more powerful TTS had a 995cc engine with two twin choke Solex carburetters.

The largest of these NSU saloons were the Type 110 and NSU 1200 with a 1085cc and 1177 cc engines respectively.

NSU also produced the first two Wankel Engined Cars, the Spyder and the Ro80. The Company was absorbed by the Volkwagen-Audi Group (Around 1977).Their final design for a conventional watercooled front engine later appeared as the Volkswagen K70.

Car Name Year Description Number Produced
Prinz I to III 58-62 First of the Post WW2 cars. 583cc two cylinder rear engine. 23bhp.
T wo doors and 4 seats but not much rear leg room.
Prinz I - 1,648
Prinz II/II(E) 31,910
Prinz III 30,678
Prinz 4 61-72 598cc two cylinder rear engine. 30 bhp. More rear room than the Prinz I to III 625,171
(possibly 625,032)
Sport Prinz 59-67 Two cylinder rear engine. 583cc to 1961 then 598cc. Sportcar styling.
(incl. 2715 made by Bertone Italy)
Prinz 1000 64-72 996cc 4 cylinder engine. Two doors. Rebadged from Prinz 1000 to NSU1000 in 1967
with minor bodywork changes. 43bhp and 40bhp respectively.
(possibly 192,161)
Prinz 1000TT 65-67 1085cc transverse aircooled rear engine. Twin carburetters. 55 bhp. 11,457
NSU TT 67-72 1177cc transverse aircooled rear engine. Twin carburetters. 65 bhp. 52,082
NSU TTS 67-72 996cc transverse aircooled rear engine. 70 bhp. Very rare. 2,402
(Possibly 2,405)
NSU Typ 110/1200 65-72 1085/1177cc. Transverse aircooled rear engine.
Longer version of the NSU100 with more luggage space at the front. Two door.
62,502 / 267,600
NSU Wankel Spyder 64-67 First of the two Wankel engined NSUs. Open top version of the Sport Prinz bodyshell.
Rare and suffered from engine problems. SEE BELOW FOR DETAIL
Various reports say 2375,
or 3000 to 5000
NSU RO80 67-77 Second Wankel engined NSU. Four door limousine. SEE BELOW FOR DETAIL 37,395 (possibly 33,900
or 37,406)

NSU Engine Development - Introduction

Dr Felix Wankel (Left), Dr Walter Froede (Right)

In 1951 contacts were established with Felix Wankel. Dr Walter Froede was the first to visit. He was director of NSU's motorcycle racing program. It was his recommendation that led to NSU's collaboration with Dr Wankel.

DKM supercharger (Left)

Wankel's first work was on rotary valves and rotary superchargers. One of his designs was attached to a 50cc NSU motorcycle, boosting the air pressure 45psi to increase the horsepower to 13.5 bhp. This cycle set a world speed record for its class of 120 mph at the Bonneville salt flats.

By 1953 Froede had become head of research and development. NSU's head engineer was against rotary engine development, but a year later Wankel and Froede persuaded the board to allow engine research if Wankel would share the patents and not receive any increase in consulting fees.

NSU Engine Development - DKM motor

In this design the rotor housing spins around the rotor (which also spins)
This allows extremely high RPM (the prototype NSU units were tested to 17000 rpm), however the design is much more complicated (eg the engine must be disassembled to change the spark plugs!)

DKM operating principle (Left)

The basis of the DKM type engine is that both the rotor and the housing spin around seperate axises. By some magic of geometry the rotor meshes with the rotor housing and there is a changing chamber volume which will allow the engine to run by the normal combustion process.
I find this concept easier to understand by using a standard mazda eccentric shaft, rotor and housing. If you hold the eccentric shaft in a vice, you can spin the rotor housing around and the rotor will turn inside the housing. Note that both the rotor and the housing spin around seperate axises (the rotor on the big lobe of the eccentric shaft and the housing around the eccentric shaft bearing).
In summary, the DKM works exactly the same as the KKM (standard rotary), but is reversed as the "eccentric shaft" is stationary and the rotor housing moves.

Because all the components in the DKM spin around their own axis they can be completely "naturally/internally" balanced (just like a turbocharger wheel which can spin at 100,000+ rpm with no vibration), the engine does not need any counterweights (like a Mazda rotary does). This allows RPM levels limited only by the strength of the metal - even back in 1957 they attained 17,000 rpm. Perhaps using current materials 40,000 rpm would be possible.

In spring 1954 Felix Wankel in conjunction with his long time associate Ernst Höppner, realised that a triangular rotor running in an epitrochoidal bore could form the basis of a four stroke cycle engine. (This was after discarding a four-lobed design.)

DKM 54 engine (Left)

The experimental unit was named the DKM 54

Testing began in January 1957. Unfortunately management had personality conflicts with Wankel so he was not invited on February 1, 1957 when the DKM 54 was fired up for the first time on the third try. The fuel was based on methanol. Gasoline was first used in April, yielding 15 bhp at 9000 rpm. The engine ran for two hours by the end of May at 21 bhp. By June 1958 it had survived a 100 hour test.

The chamber volume was 125 cc., best performance 29 hp (DIN) at 17000 rpm, engine diameter only about 260 mm, shaft offset 9.5 mm. Three spark plugs rotated with the inner rotor.

Four units were built but the DKM 54 remained the only NSU DKM type engine ever constructed. One of them got its due place in the Neckarsulm (Germany) Museum.

NSU Engine Development - KKM Motor:

This is the "conventional" rotary design where the rotor housing is fixed and the rotor spins inside the housing. (as used by Mazda etc)

In 1957 NSU abandoned the original DKM concept as it was was far too complex a mechanism ever to go into production and all further research work was concentrated on the planetary rotation KKM type, which was invented by Dr Froede

KKM engine ("Conventional Rotary")

This was a fundamental change to Felix Wankel`s original idea and in this way the very high engine revolutions were partly lost. It was also not as smooth and had more sealing problems (since the apex seals experienced greater forces because the rotor orbited the stationary gear.) However it had other advantages, not the least of which was the engine did not have to be disassembled to change the spark plugs

Felix Wankel is reported to have said that they had transformed his racing horse into a cart horse.

KKM 250 (Left)

In 1958 two engine types were built and successfully tested. This confirmed the principle of the KKM system. As of 1960 an experimental KKM 250 was fitted into the small NSU Prinz. The engine output was approximately 30 hp (DIN) at modest 5000 rpm. Between 1960 and 1964 a large number of engine types was developed and installed into a variety of applications ranging from lawn mowers to boats.
KKM 502 (Left)

The provisional result was the KKM 500 which became operational in the NSU Spider as type 502. However, further development and introduction to the public was delayed because of serious technical problems which arose from the gas and oil sealings and other components.
Peter Hofbauer made a five chamber KKM which later became a compressor. His design is said to be the only rotary engine without a low pressure stage to function as a diesel engine.


NSU/Wankel Licencing

Many manufacturers showed interest in the new rotary engines because they were smooth, powerful (for their capacity) and had the potential to be easily manufactured. As NSU had the rotary engine patented, companys wishing to make their own Wankel rotary engines were required to pay a licensce fee.
26 organisations licensed the Wankel - The first was Curtis-Wright on October 21, 1958/second Fichtel & Sachs/third Yanmar Diesel/fourth Toyo Kogyo (Mazda) on February 27, 1961

NSU required license holders to share research results with all others (although GM obtained an exemption). This was important because there were only seven years between the first engine test and the first production automobile, compared with nearly a hundred years of development of the piston engine.
Early on NSU was shocked by how quickly Toyo Kogyo (Mazda) was developing engines.
Interestingly, this sped NSU development because Mazda did not have to pay any fees until NSU offered a car for sale that could reliably run 50,000 kilometres.

NSU Wankel Spider, 1964-1967

NSU Spider

NSU Spiders

NSU Spiders

NSU Spider

KKM 502 engine
(Single rotor)

KKM 502 engine
(Single rotor)

KKM 502 engine
(Single rotor)

NSU first road tested the Wankel in 1960, later that year they showed a preliminary version of the Spider at a Munich meeting of German engineers. Wankel spoke to the conference and won over the many skeptics in the audience.

The production NSU Spider was unveiled at the 1963 Frankfurt Automobile Show and was the first car to be powered by a Wankel rotary engine. The car was a convertible version of the "sport prinz", styled by bertone and was normally fitted with a 598cc 2 cylinder piston engine.
NSU aimed at the motoring enthusiast, against the likes of the Austin Healy Sprite etc, and in some respects the Spider was a continuation of their Wankel engine development programme. Full production started only in autumn 1964. Up to 1967 about 2375 units were produced (Some reports say anywhere between 3000 and 5000), of which about 100 are still in operation in Germany. Specially tuned Spiders were also serious competition cars and gained titles at rallies and hillclimb races.
The Spider was 3.58m in length and weighed 700 kg, and gave lots of driving pleasure at modest fuel consumption. The top speed was over 150 km/h. There were front disc brakes, a black hard top was available for winter and buyers could choose between a red or white finish.

The single-rotor engine type KKM 502 had a 498 cc chamber volume and developed approx:
50 bhp at 5000 rpm
54 bhp at 6000 rpm
52 lb-ft at 2500 rpm
54 lb-ft at 3000 rpm
57 lb-ft at 3500 rpm
The engine was mounted under a separate cover of the rear luggage compartment, and the water cooling system was in the front part of the car.

All normal spiders had a 50 HP engine, with a little special series of rallye and racing cars with a factory tuned motor with 65 HP at 7500 rpm.

NSU Ro80, 1967-1977

NSU Ro80 Sedan
NSU KKM612 2 rotor engine

NSU KKM619 experimental
3 rotor engine (808x746)

Development of the Ro80 began in August 1961 and it was officially shown at the 1967 Frankfurt Auto Show.
The design was quite advanced for its time, with front wheel drive, fully independent suspension, four wheel disc brakes with dual hydraulic circuits and a semi-automatic gearbox. Aerodynamic drag coefficient was 0.35, amazingly low for its time, though this was ultimately 0.39 with larger tires and cooling openings. The weight distribution was 63/37 front/rear it handled very well. The chief stylist was Claus Luthe.

The car was well received by the public and the press, however it suffered from major engine problems which resulted in the demise of the company. Some cars were converted to conventional V4 engines (I think these were Ford V4s from England/Germany). However modern materials have fixed some of the engine reliabilty problems (using modified Mazda parts), some Ro80s are being converted back to their former glory.

Originally the Ro80 it was to have a two rotor engine with 2 x 300cc capacity (that is, a two rotor version of the single rotor KKM 502 engine used in the spider - this version was called the KKM 512). However the production motor for the Ro80 was revised to the 2 x 497cc KKM612, which was the first and only factory 2-rotor peripheral ported Wankel engine. The peripheral ports were chosen for high speed use on Germany's autobahns.

There was three rotor successor being planned in 1969 using the KKM619 3 rotor engine with 3x 498 cc chambers, producing around 150-180 bhp (pictured above). However this was when the Audi/VW takeover occured, so development ceased.

Engine type: KKM 612
Capacity: 2 x 497cc
1967 model Power: 129 hp at 5500 rpm
1973 model Power: 115 bhp DIN at 5000 or 5500 rpm
1973 model Torque 112 lb-ft at 4500 rpm
Weight 2955 lb (2668 lb)
Top Speed 112 mph
Price DM 14,150
(Note these specifications have come from several sources, so may not be 100% accurate. One source says the engine makes 136hp)

The downfall of NSU

On 10th March 1969, NSU and Audi (100 % owned by Volkswagen) formed Audi-NSU Autounion AG. (The name NSU was dropped from the company name in 1984, at which time NSU GmbH was formed as a seperate company). Internal politics, finances and conservatism snuffed out rotary development and hence production of the Ro80 ceased and the assembly line re-tooled to produce Audi models.
The fact that the engines used in the Ro80 were failing at low milages did not do NSU any good, as NSU had rushed the Ro80 into production to try and beat Mazda. Unfortunately the rush did not allow the engineers enough time to work out all the bugs with the motor and it's materials. Due to their determination to be a technological leader, NSU was not making any conventional piston engine cars at the time, so there were no reliable piston models to fall back on (unlike Mazda), so the marque disappeared.

NSU Gmbh still exists, although they do not make anything (they have a staff of 3-the boss and 2 secretaries). In 1997 the factory celebrates its 100th birthday. It is rumored they have one new car left in the stores compound (either yellow or orange in colour) which has been there since the company ceased production.

More Information

I do not know a lot about NSU engines and cars. Much of the information here has been compiled from other places around the net, as when this page was originally written there was little available in English. The text has been re-written in my words. If there is any pictures belong to you (and you don't like it) let me know and I will remove it.

Further reading and acknowledgements:
* Special thanks to Gerhard Geiling for sending me information for this site.
* Try a library for one of the many books written in the 70s about the rotary engine and it's makers

Other relevant reading at Craig's Rotary Page (Please go via the INDEX page):
* No other pages on this site are relevant to NSUs

Other relevant sites on the Internet (Please go via the LINKS page):
* Gerhard Geiling has a very extensive NSU website
* There are a number of other sites about NSU in my links section.

This page last updated 17/3/2001
Update History:
13/12/2001 - Fixed a few broken photos and tidied up a bit.
17/3/2001 - Modified More Information section, Spell check, Converted all text to new standard (Headings as Heading1, Some sub-headings (e.g. tables) as 14 point normal bold italic, Most text as Normal, Internal page links at top not all uppercase), Changed from Netscape to FrontPage. Background image changed to PG00_02B.JPG
31/10/1997 - Previous known update (May have been some before this)

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