Production Of The Wankel Rotary Engine Engineering Essay

Conceived in the 1930s, simplified and successfully tested in the 1950s, the favorite of the automotive industry in the early 1970s, so all but abandoned before resurging for a superb tally as a high-performance power works for Mazda, the Wankel rotary engine has long been an object of captivation and more than a small enigma. A unusually simple design, it boasts compact size, light weight and about vibration-free operation. ( Hege 2001 )


Nikolaus August Otto of Germany succeeded in doing a practical internal burning engine in 1876, in 1886 first car using an internal burning engine was made. Since so, the development of the internal burning engine for automotive intents has been singular.

The history of internal burning engine chiefly consisted of engines that possessed the reciprocating mechanism. But as the affair of fact, there have been legion challenges made, in the class of development of the internal burning engine, to make practical rotary engines. ( Yamamoto 1981 )

Already around 1636, a German called Pappenheim sketched a rotary pump, which was used about 150 old ages subsequently in Watt ‘s steam engines for the first clip in pattern. These machines had many troubles that could non be solved at that clip.

Finally a German mechanical applied scientist, Felix Wankel ( 1902 – 1988 ) , succeeded to work out the most hard job of rotary engines, waterproofing of the rotor. He could besides reply the inquiry of the best form. A German motor maker, NSU Motorenwerk AG at Neckarsulm, supported him a batch through out his undertaking boulder clay in 1967 the first auto utilizing a Wankel engine, the NSU Ro 80, was produced. ( Hutten 1982 )

Development of Wankel engines went on so that in early 1970 ‘s the stock of companies keeping pieces of Wankel engineering were mounting. Major car executives were publically foretelling, “ In ten old ages, the full car industry will be 95 percent traffic circle ” ( Hege 2001 ) .

Problem Statement

Because reciprocating engines were non efficient and dependable plenty at the clip they started out, applied scientists started seeking for an alternate design.

A reciprocating internal burning engine uses the force per unit area of spread outing gas to travel a Piston through a cylinder ; the Piston is connected to a crankshaft by a connecting rod to change over its back-and-forth motion into a much more utile round gesture. Adding the valves system to this, we have a really complicated constellation. Here comes the job statement of rotary engines, the reciprocating engine ‘s have excessively many traveling parts. Decades ago constructing an engine that would bring forth any sort of utile power meant stretching the bounds of stuffs and design. As power goes higher the opportunities of the parts to interrupt goes higher and this brings faithfully down. ( Wankel 1965 ; Hege 2001 )

What is the solution? The solution is a new type of gasolene engine, a simpler engine with less traveling parts. A rotary engine.

So many constructs came and went, some attracted more attending than others but the merely successful design that made it into mass-production is the Wankel rotary engine.

Principles of rotary engine

The Wankel rule is so similar to Otto engine rule, merely difference is Wankel uses a trochoidal ( almost-triangular ) rotor traveling about in an epitrochoidal ( about egg-shaped ) hosing to make the four rhythms. ( Hege 2001 )

Here is a brief account of how the four rhythms go on in a rotary engine:

Fig. 1

Each of the three faces of rotor is undergoing a different stage of a four-cycle engine. In this illustration, the consumption is now closed on side A and compaction is get downing. Side B has about reached the terminal of the enlargement rhythm, and side C has finished exhausting and is get downing a new consumption rhythm.

Fig. 2

Side A is nearing maximal compaction.

Side B has opened to the fumes port, and side C is go oning its consumption shot.


Side A is at maximal compaction. Ignition happens at this phase.

Side B has merely opened the exhaust port, and side C is unfastened to the consumption port and is pulling in fresh mixture.

Fig. 4

Side A is being driven by burning.

Side B is coercing out the spent fumes gas, and Side C is at peak volume and the consumption port is about to shut.

By the clip the bizarre shaft has moved through 360A° of rotary motion, the rotor will merely hold moved 120A° . ( Wankel 1965 ; Yamamoto 1981 ; Hege 2001 )

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Some chief eyeglasses that Wankel had in his head are:

A on the job rotary form engine that has to carry through Otto four-stroke rhythm in a rotating chamber.

An engine power of at least equal to the existed reciprocating engines.

Smaller in size and igniter in weight comparison to reciprocating engines.

Not many traveling parts due to the job of breakage.

Not holding a complicated valve system due to the complicacy of it and once more to extinguish traveling parts.

Partss working in high temperature and high force per unit area environment.

Get the better ofing the sealing job between two skiding metals. ( Yamamoto 1981 ; Hege 2001 )

Research and thought coevals

Wankel started experimenting by modifying bike engines with different designs, so he worked on a traffic circle compressor which had the potency of being converted to a four-stroke engine. He had two chief jobs with his engine ; one was the waterproofing job which was the chief job of these types of engines and the other was to happen the best form of rotor and lodging.

To work out the first job Wankel started analyzing Piston rings which were still being discovered at the clip but cipher understood them better than Wankel. He had learnt a batch about cylinder sealing during his ain experiments and was seeking to use what he had learnt to his disc valve design. The job of sealing a chamber is similar to sealing a cylinder but the forms are non. Circles are much easier to bore, stopper or seal than consecutive lines or irregular forms. Wankel tried a big organic structure of forms and stuffs under different spring tenseness to happen the best. In most instances spring force per unit area needed was truly rather low because the force of the gas bring forthing most of the force per unit area needed for sealing.

So Wankel developed other significances of shuting the spreads, for irregular gaps, he designed metal strips that would lie, inter-linked with cylindrical articulation components. ( Fig. 5 ) Using this system he could seal about any molded port. ( Hege 2001 )

Fig. 5 ( Hege 2001 )

Wankel ‘s packing organic structure seals which are so similar to piston rings.

They were made of movable parts fitted into finely machined channels.

A web of strips connected by peg-like trunnions enabled him to seal any form of opening against a traveling surface.

The alone form of Wankel ‘s engine is built around the lines drawn by turn overing one circle around another. His basic form is described by taking a bring forthing circle of radius equal to one half the radius of the basic circle. The resulting form will be the two-lobe epitrochoid, the form of the Wankel ‘s working chamber. ( Fig. 6 ) ( Yamamoto 1981 ; Hege 2001 )

Fig. 6 ( Hege 2001 )

As the cogwheel ratio was two to three, revolving the outer gear around the inner traced way of the epitrochoid that made the working lodging. ( Yamamoto 1981 )

The elaborate design work

There are some footings Wankel used for his new form:

Fig. 7 ( Hege 2001 )

A=minor axis ; B=major axis ; 1,2,3=working Chamberss ; C=mainshaft Centre ; D=eccentric Centre ; E & A ; F=phasing cogwheels ; G, H, I=Rotor apexes ; J, K, L=rotor conventions ; M= point where rotor conventions intersect and besides intersection of phasing cogwheels ; I?= tilting angle of apex seals ; distance D-H=radius of rotor.

Ratio of = = K factor

Wankel besides tried three-lobe lodging alternatively of two in his experiments but his early experiments were done without any mathematical analysis. Professor Othmar Baire did the mathematical analysis and found that the possibility of different forms was practically eternal, but Wankel focused on the feature of compaction potency and the tilting angle of the vertex seals.

K factor ( the ratio of the radius of the rotor divided by the eccentricity of the engine ) plays an of import function, one time the K factor is determined by the interior decorator, the fluctuations in compaction are limited by the engine ‘s dimension. If the K factor is low, the engine can be really little for its supplanting, but its possible compaction will be low and the apex seal tilting angle will be really high as the seals must traverse a really tight chamber waistline. Most practical Wankel applications have a K factor between 6 and 10 as applied scientists try to happen a via media between physical size, seal propensity angles and many other considerations that come into drama. ( Yamamoto 1981 ; Hege 2001 )

First working engine

By work outing the chief jobs of the engine, Wankel with the aid of his old friend, Ernest Hoeppner, eventually converted his compressor to a working engine, it took them over three old ages to make so. But this merchandise was barely close to what we know as the Wankel traffic circle. The first engine was labeled DKM54 in February 1957, 54 bespeaking the supplanting in three-dimensional metre. But this was merely a trial paradigm which had so many jobs such as complicacy of the forms to seal. But Wankel had spent so many old ages developing a waterproofing system for his engine and here was his chance to prove it. The most of import portion to seal was the apex seal, because at any clip, all three rotor faces are engaged in different parts of engine ‘s on the job rhythms. It is the occupation of the vertex sealing to maintain these procedures separated from each other. ( Hege 2001 )

Fig. 8 shows the Wankel ‘s original vertex waterproofing.

Fig. 8 ( Hege 2001 )

Wankel ‘s original vertex sealing which used strips of a sealing stuff, drive in channels cut into the rotor tips.

They are lightly jumping loaded, to help sealing merely in start up.

When the engine is running, the centrifugal force on the seals is adequate to maintain them pressed against the surface of the interior rotor.

A few month after the DKM54 a larger version was built, the DKM125. ( Fig. 9 ) But neither the DKM54 nor the DKM125 was at all practical because the Centre shaft was stationary. Walter Froede, NSU head applied scientist, was already working on that job, while the DKM motor was being built Froede began work on a modified version, he converted the outer rotor to a stationary lodging and made the cardinal mainshaft a traveling piece which would be the end product shaft. The new engine was dubbed the KKM125. ( Fig. 10 ) ( Hege 2001 )

One of the issues of these types of engines at this clip was to measure the supplanting and sort the Wankel. Not merely for the applied scientists themselves, even for the authoritiess, because they must revenue enhancement anything that moves. Later it would besides go of import for rushing functionaries as they tried to make up one’s mind where to let the Wankel-engined autos to vie. After tonss of treatments everyone agreed to multiply the maximal chamber volume by two and multiply that figure by the figure of rotors.

The new KKM125 engine besides introduced its ain set of jobs such as quiver of the engine ( it was non as wholly vibration-free as the original traffic circle ) and turbulency of oil inside the rotor ( the rotor was oil cooled ) . ( Hege 2001 )

Froede and his staff worked on all these jobs till a well-developed version of the KKM125 developed 26 HP at 11,000 revolutions per minute, a respectable end product for an engine that merely weighed 37.5 lbs ( 17 Kg ) . By mid-1959, a larger version ( KKM250 ) was built and undergoing testing.

Finnaly in 1960, the 250 was installed in a standard NSU Prinz, a basic sub-compact auto already in production. It did drive but it was rough and hard to drive, and it proved that the Wankel could be adapted to automotive usage. Subsequently the KKM400 was built, a larger version of the KKm250. It could bring forth 40 to 50 HP. The NSU Sport Prinz was produced which was easier to drive, smoother and more powerful. ( Hege 2001 )

Fig. 9 Patent drawings for Wankel ‘s DKM engine ( Hege 2001 ) Fig. 10 Patent pulling for the KKM engine ( Hege 2001 )

Further development

On October 21, 1958 Curtiss-Wright ( an American aircraft and engine fabrication company ) became the first company to buy a licence to bring forth Wankel engines for $ 2.1 million and a 5 per centum committee on all Wankel engines that Curtiss-Wright would construct or sell. Curtiss-Wright applied scientists started analyzing all facets of Wankel design, they had settled on a design of 60 three-dimensional inches, IRC6, which developed 100 HP at 5500 revolutions per minute in its first dyno trial, in 1959. ( Hege 2001 )

In 1963, Charles Jones began work on a duplicate rotor version of RCI60 ( sport version of IRC6 ) , it was named RC2-60 U5.

Curtiss-Wright applied scientists worked a batch on the jobs of their engines and eventually in 1965 the RC2-60 engine reached a point in its development where it was comparable to piston type car engines. A 1966 Ford Mustang was the first trial auto for the RC2-60 U5 engine. It was tested by Jan Norbye, automotive editor for Popular Science magazine. ( Hege 2001 )

“ It had a steady idle at 800 revolutions per minute and a tap on the throttle sent the rpm up to 2000 in a flash. Above 2000 revolutions per minute it began to develop a new sound, a sound I had ne’er heard beforeaˆ¦ .

As the engine began to weave, the pitch was lower than turbine ‘s, although there was something of a turbine in it. Yet it had the equally throbing beat of a good six in perfect tuneaˆ¦without any indicant of making top velocity when pushed to the 6000 grade. It would apparently travel on and on speed uping everlastingly. “ ( Jan 1966 ) ( p. 102-107 )

Max Bentele ( a German applied scientist working for Curtiss-Wright ) designed and developed the first four-rotor Wankel engine ( 4RC-6 ) which produced 425 HP at 6500 rpm. ( Fig. 11 ) ( Hege 2001 )

Fig. 11 Patent drawings of Curtiss-Wright ‘s four rotor Wankel designed by Max Bentele ( Hege 2001 )

By 1966 Curtiss-Wright had designed, developed and tested Wankel engines from one extreme to the other. They were the first to construct a multi-rotor engine, and they had built the largest ( 1920 cubic inches, 872 HP at 1525 revolutions per minute ) and the smallest ( 4.3 three-dimensional inches, 3.5 HP at 4000rpm ) Wankels yet. ( Hege 2001 )


In October of 1960, Matsuda president of Toy Kogyo ( Mazda ) and five of his proficient staff went to Germany to work on an understanding with NSU. On October 12 the understanding was signed and a KKM400 paradigm engine, with programs and drawings were sent to Toyo Kogyo.

Kenichi Yamamoto ( main applied scientist of Wankel undertaking ) believed that the rotary engine ‘s jobs were because the metallurgy and machining engineering of the clip were non up to the traffic circle ‘s advanced design, so he gathered a little squad of metallurgical engineer, interior decorators and applied scientists to analyze and work on the jobs existed. They approached the jobs by experimenting with new stuffs and techniques for utilizing them, trusting to happen the right combination. ( Hege 2001 )

In 1961 they built their first production theoretical account, 110S, after holding a heap of about 5,000 debris rotary engines. It was designed with light-alloy rotor, iron terminal screens and aluminium trochoidal lodging. The surface of the lodging was electroplated with Cr. This produced difficult, smooth surface for the seals to sit on. The seals were reasonably soft, made of a carbon-aluminum complex. They solved most of the jobs merely by taking the right stuff for the occupation. They besides found some new techniques to do the production faster and therefore cheaper. ( Such as the graft coating procedure, which reduces the clip that the trochoidal lodging has to pass in the Cr plating armored combat vehicle ) . ( Hege 2001 )

In 1963 Mazda had its first paradigm of production rotary auto, The Mazda Cosmo. ( Fig. 12 )

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Since so Mazda has been bring forthing many different types of Wankel-powered autos and is the lone Wankel rotary manufacturer today ( RX-8 ) .

There were so many other companies bought the Wankel ‘s licence such as Fichtel & A ; Sachs AG, Yanmar Diesel Co. Ltd. , Daimler-Benz AG, Rolls-Royce Ltd, and etc. ( Hege 2001 )

Some of merchandises produced by these companies are, NSU RO 80, the Citroen M35, the Mercedes-Benz C111, and etc.

Emission ordinances

In 1970, Nixon established two new bureaus for the intent of researching and implementing authorities environmental policy, EPA ( Environmental Protection Agency ) , and NOAA ( National Oceanic and Atmospheric Administration ) .

With the transition of Air Pollution Control Act of 1970, emanation criterions for automotive fumes were set. ( Hege 2001 )

Up until now, the Wankel had been considered a comparatively “ dirty ” engine, with HC ( unburned hydrocarbons ) end product about three times that of a Piston engine, largely because of the high surface to volume ratio of a Wankel engine. Other harmful constituents of car fumes are carbon monoxide ( CO ) and oxides of N ( NOx ) .

To work out this job surveies started at University of Michigan with the petition of Curtiss-Wright.

Experiments at the University of Michigan focused on the usage of a thermic reactor and air injection to clean up the fumes after it left the engine.

A thermic reactor is fundamentally a heat range, which keeps the fumes temperature up so that the staying fuel ( HC ) is burned up. In most designs, excess air is pumped in at the engine fumes port to keep the reaction. Many trials were done on an RC2-60 U5 and the consequences proved that utilizing the thermic reactor and air pump reduces the HC content by 90 per centum, so Curtiss-Wright Wankel engine could be gone in the market with current Torahs. ( Hege 2001 )

At he same clip Mazda besides was working with a thermic reactor and air pump system. They besides achieved good consequences with their twin sparkplug system, as they could close down the trailing ignition during certain operations ( Fig. 13 ) . Consequences were so positive that in the spring of 1972, they announced their engines would hold no problem meeting 1975 U.S. emanation criterions. ( Hege 2001 )

Figure 13 ( Hege 2001 )

Upcoming engineering even made the Wankel expression even better, therefore American companies like General Motors and Ford were more interested in Wankel engines. But among all these American companies Mazda became the most successful company in selling traffic circles in America. While in 1970 Mazda sold merely 2000 autos, in 1971 they sold 21000 and in 1972 62000. And they openly predicted selling 300,000 autos in America in 1975. ( Hege 2001 ) But things did n’t travel on as they expected.

The EPA tested Mazda ‘s autos and the consequences showed a gas milage of merely over 10 stat mis per gallon in metropolis drive. Mazda did n’t desire to accept this figure and they published their ain figures, but in clip of high gas monetary values, the harm was done, and the Mazda traffic circle had become ill-famed as a gas guzzler. Other jobs of Mazda ‘s autos were the early dislocation and besides non being of adequate rotary mechanics. In January of 1974, gross revenues fell off by over 50 per centum from the twelvemonth earlier. ( Hege 2001 ) This was about an terminal for Mazda traffic circle as a rider auto but future selling would be to concentrate on the traffic circle ‘s qualities as a high public presentation engine.

While other companies were dropping their rotary plans, Mazda held on until it was the lone major maker of rotary engines left. They worked on it and improved their engine ‘s gas milage and dependability and introduced their rejoinder auto in May of 1978, the RX7, a two-seat athletics coupe which put the traffic circle in the public presentation market where it belonged.

Wankel, as it is, has done good, it made a niche for itself in markets where high power to burden ratios are of import. It is acquiring better and better as the stuff scientific discipline progresss and it might someday be able to fit the efficiency of Piston engines.

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Hege, J. B. ( 2001 ) . The Wankel rotary engine: a history, McFarland & A ; Company, Inc. , Publishers.

Hutten, H. ( 1982 ) . “ Motoren. ” from hypertext transfer protocol: // v=2.

Jan, N. ( 1966 ) . “ Test Drive of US Car with a Revolving Combustion Engine. ” Popular Science ( April 1966 ) : 102-107.

Wankel, F. ( 1965 ) . Rotary Piston Machines, ILIFFE BOOKS LTD.

Yamamoto, K. ( 1981 ) . Rotary Engine. Tokyo, Japan, Sankaido Co. , Ltd.