Rotary piston engine working principle. Motors for aviation, "eights" and "nines"

21.04.2019

steam engines and internal combustion engines have one common drawback - the reciprocating movement of the piston must be converted into rotational movement of the wheels. Hence the obviously low efficiency and high wear of the mechanism elements. Many wanted to build an internal combustion engine so that all moving parts in it only rotated - as happens in electric motors.

However, the task turned out to be not easy, only a self-taught mechanic, who in his entire life never received a higher education, or even a working specialty, managed to successfully solve it.

There is a legend that the solution to the problem came to the seventeen-year-old Felix in a dream. Whether this is true or not is unknown. But it is obvious that Felix had a very outstanding ability to mechanics and a "non-soapy" look at things. He understood how all four cycles of a conventional internal combustion engine (injection, compression, combustion, exhaust) can be carried out while rotating.

Quite quickly, Wankel came up with the first engine design, and in 1924 he organized a small workshop, which also served as an impromptu "laboratory". Here Felix began to conduct the first serious research in the field of rotary piston internal combustion engines.

From 1921, Wankel was an active member of the NSDAP. He advocated party ideals, was the founder of the All-German Military Youth Association and the Jungführer of various organizations. In 1932, he left the party after accusing one of his former colleagues of political corruption. However, on a counter-charge, he himself had to spend six months in prison. Released from prison thanks to the intercession of Wilhelm Keppler, he continued to work on the engine. In 1934 he created the first prototype and received a patent for it. He designed new valves and combustion chambers for his motor, created several different versions of it, developed a classification of kinematic schemes for various rotary piston machines.

In 1936, BMW became interested in the Wankel engine prototype - Felix received money and his own laboratory in Lindau to develop experimental aircraft engines.

However, until the very defeat of Nazi Germany, not a single Wankel engine went into production. Perhaps to bring the design to mind and create mass production it took too long.

After the war, the laboratory was closed, the equipment was taken to France, and Felix was left without a job (his former membership in the National Socialist Party affected him). However, Wankel soon got a position as a design engineer at NSU Motorenwerke AG, one of the oldest manufacturers of motorcycles and cars.

In 1957, through the joint efforts of Felix Wankel and NSU lead engineer Walter Froede, a rotary piston engine was first installed on the NSU Prinz car. The initial design turned out to be far from perfect: even to replace the candles, it was necessary to disassemble almost the entire “engine”, reliability left much to be desired, and it was a sin to talk about efficiency at this stage of development. As a result of the tests, a car with a traditional internal combustion engine went into the series. Nevertheless, the first rotary-piston engine DKM-54 proved its fundamental performance, opened up directions for further refinement and demonstrated the colossal potential of the “rotors”.

Thus, a new type of internal combustion engine finally got its start in life. In the future, it will have many more improvements and improvements. But the prospects for a rotary piston engine are so attractive that nothing could stop engineers from bringing the design to operational excellence.

The design of a rotary piston internal combustion engine allows you to implement any four-stroke cycle without the use of a special gas distribution mechanism. Thanks to this fact, the "rotor" turns out to be much simpler than a conventional four-stroke piston engine, in which, on average, there are almost a thousand more parts.

The sealing of the working chambers in a rotary-piston internal combustion engine is provided by radial and end sealing plates pressed against the "cylinder" by tape springs, as well as by centrifugal forces and gas pressure.

Another one of his technical feature is high labor productivity. For one complete revolution of the rotor (that is, for the cycle "injection, compression, ignition, exhaust"), the output shaft makes three complete revolutions. In a conventional piston engine, such results can only be achieved using a six-cylinder internal combustion engine.

After the first successful demonstration of a rotary internal combustion engine in 1957, the largest auto giants began to show increased interest in the development. At first, the license for the engine, which received the informal name "Wankel", was bought by Curtiss-Wright Corporation, a year later, Daimler-Benz, MAN, Friedrich Krupp and Mazda. In just a very short period of time, about a hundred companies around the world have acquired licenses for the new technology, including such monsters as Rolls-Royce, Porsche, BMW and Ford.
Such interest in the "wankel" of such large players in the automotive market is due to its great potential and significant advantages - a rotary piston engine has 40% fewer parts, it is easier to repair and manufacture.

In addition, the Wankel is almost twice as compact and lighter as a traditional piston ICE, which in turn improves the car's handling, facilitates the optimal location of the transmission and allows for a more spacious and comfortable interior.

The rotary piston engine develops high power with a rather modest fuel consumption. For example, a modern "wankel" with a volume of only 1300 cm³ develops a power of 220 hp, and with a turbocharger - all 350. Another example is miniature engine OSMG 1400 weighing 335 g (5 cm3 working volume) develops a power of 1.27 hp. In fact, this little one is 27% stronger than a horse.

Another important advantage is the low level of noise and vibration. The rotary piston engine is perfectly balanced mechanically, in addition, the mass of moving parts (and their number) in it is much less, so that the "Wankel" runs much quieter and does not vibrate.

And finally, the rotary piston engine has excellent dynamic characteristics. In low gear, without much load on the engine, you can accelerate the car to 100 km / h for high revs engine. In addition, the Wankel design itself, due to the lack of a mechanism for converting reciprocating motion into rotational motion, is able to withstand higher speeds than a traditional internal combustion engine.

After the NSU Spyder released in 1964, the legendary NSU Ro 80 model followed (there are still many clubs of owners of these cars in the world), Citroen M35 (1970), Mercedes C-111 (1969), Corvette XP (1973). But the only mass manufacturer was the Japanese Mazda, which has been producing since 1967, sometimes 2-3 new models with RPD. Rotary engines were put on boats, snowmobiles and light aircraft. The end of euphoria came in 1973, at the height of the oil crisis. It was then that the main drawback of rotary engines appeared - inefficiency. With the exception of Mazda, all automakers ended rotary programs, and the Japanese company's sales in America fell from 104,960 cars sold in 1973 to 61,192 in 1974.
Along with undeniable merits, "Wankel" also had a number of very serious shortcomings. First, durability. One of the first prototypes of rotary-piston engines ran out of service in just two hours. The next, more successful DKM-54 had already endured a hundred hours, but this was still not enough for the normal operation of the car. The main problem lay in the uneven wear of the inner surface of the working chamber. During operation, transverse furrows appeared on it, which received the speaking name "devil's marks".

At present, the problem of reliability and durability has been finally solved by using high-quality wear-resistant coatings, including ceramic ones.

Other serious problem- increased toxicity of the Wankel exhaust. Compared to a conventional reciprocating internal combustion engine, a “rotornik” emits less nitrogen oxides into the atmosphere, but much more hydrocarbons, due to incomplete combustion of fuel. Quite quickly, Mazda engineers, who believed in the bright future of the Wankel, found a simple and effective solution to this problem. They created the so-called thermal reactor, in which the hydrocarbon residues in the exhaust gases were simply “burned out”. The first car to implement this scheme was the Mazda R100, also called the Familia Presto Rotary, released in 1968. This car, one of the few, immediately went through very tough environmental requirements, put forward by the US in 1970 for imported cars.

The next problem of rotary piston engines partially follows from the previous one. This is economy. The fuel consumption of a standard "wankel" due to incomplete combustion of the mixture is significantly higher than that of a standard internal combustion engine. Once again, Mazda engineers set to work. With the help of a whole range of measures, including the processing of the thermoreactor and carburetor, the addition of a heat exchanger to exhaust system, the development of a catalytic converter and the introduction of a new ignition system, the company achieved a 40% reduction in fuel consumption. As a result of this undoubted success, in 1978 was released sport car Mazda RX-7.

Soviet officials negotiated with Felix Wankel for quite some time regarding the purchase of licenses, some of which took place right in Moscow. True, no money was found, and therefore it was not possible to use some proprietary technologies. In 1976, the first Volga single-section VAZ-311 engine with a capacity of 65 hp was put into operation, it took another five years to fine-tune the design, after which an experimental batch of 50 units of VAZ-21018 rotary "units" was produced, which instantly dispersed among VAZ workers. It immediately became clear that the engine only outwardly resembled a Japanese one - it began to crumble in a very Soviet way. The management of the plant was forced to replace all engines with serial piston engines in six months, cut the staff of SKB RPD by half and suspend the construction of workshops. The salvation of the domestic rotary engine building came from the special services: they were not very interested in fuel consumption and engine life, but they were very interested in dynamic characteristics. Immediately, a two-section RPD with a power of 120 hp was made from two VAZ-311 engines, which began to be installed on the “special unit” - VAZ-21019. It is this model, which received the unofficial name "Arkan", that we owe countless tales about police "Cossacks" catching up with fancy "Mercedes", and many law enforcement officers - with orders and medals. Until the 90s, the outwardly unpretentious Arkan really easily overtook all cars. In addition to VAZ-21019, AvtoVAZ also produces small batches of VAZ-2105, -2107, -2108, -2109, -21099 cars. Max speed rotary "eight" is about 210 km / h, and up to a hundred it accelerates in just 8 seconds.

Revived on special orders, SKB RPD began to make engines for water sports and motorsport, where cars with rotary engines began to win prizes so often that sports officials were forced to ban the use of RPD.

In 1987, Boris Pospelov, the head of the SKB RPD, died and Vladimir Shnyakin was elected at the general meeting - a man who came to the automotive industry from aviation and dislikes ground transport. The main direction of SKB RPD is the creation of engines for aviation. This was the first strategic mistake: our planes are produced incommensurably fewer cars and the plant lives off the sold engines.

The second mistake was the orientation in the preserved production of automotive RPDs to low-power VAZ-1185 engines of 42 hp. for the Oka, although more voracious, but more dynamic rotary engines are asking for the fastest domestic cars- for example, on the "eight". The same Japanese install "wankels" only on sports models. As a result, on Russian roads there were only a few rotary minicars "Oka". In 1998 was finally prepared civil version two-cylinder rotary 1.3-liter VAZ-415 engine, which began to be installed on the VAZ-2105, 2107, 2108 and 2109.

In May 1998, the ring VAZ-110 "RPD-sport" (190 hp, 8500 rpm, 960 kg, 240 km/h) was homologated. Alas, things did not go further than a single sample, more often shown at exhibitions than starting in races. The 110 was the most powerful in the peloton, but the frankly crude design each time did not allow it to demonstrate its full potential. However, the most offensive thing is that at VAZ they quickly cooled off towards the rotary direction, and the unique Lada was converted into a rally car with a conventional internal combustion engine.

So why haven't all the leading car manufacturers switched to Wankel yet? The fact is that the production of rotary piston engines requires, firstly, a well-honed technology with a wide variety of nuances, and not every company is ready to follow the path of the same Mazda, stepping on numerous "rakes" along the way. And secondly, we need special high-precision machines capable of turning surfaces described by such a cunning curve as an epitrochoid.

The Mazda RX-7 is one of the first cars to feature a Wankel rotary piston engine. There have been four generations in the history of the Mazda RX-7. First generation from 1978 to 1985. Second generation - from 1985 to 1991. Third generation - from 1992 to 1999. Last, fourth generation - from 1999 to 2002. The first generation RX-7 appeared in 1978. It had a mid-engine layout and was equipped with a rotary engine with a capacity of only 130 hp. With.

Like NSU, Mazda in the 60s. was a small company with limited technical and financial resources. The basis of its lineup was delivery trucks and family runabouts. Therefore, it is not surprising that the Mazda 110S Cosmo sports coupe (982 cm3, 110 hp, 185 km/h) was created for more than 6 years and turned out to be very capricious and expensive. And the damaged reputation of the NSU Ro80 did not contribute to the excitement (in 1967-1972 only 1175 "spaces" found their owners), but the world interest in the 110S contributed to an increase in sales of all the rest of the company's products!

To prove that the RPD is just as reliable (its superiority in power has already become obvious to everyone), Mazda took part in the competition for almost the first time in its life, and chose the most difficult and longest race - the 84-hour Marathon De La Route, held on Nurburgring. How the crew from Belgium managed to take 4th place (the second car retired three hours before the finish line due to jammed brakes), losing only to the Porsche 911 “grown up” on the Nordschleife, seems to remain a mystery.

Wankel workshop in Lindau

In the rally, the Mazda did not go so smoothly. As was often the case with Japanese teams (Toyota, Datsun, Mitsubishi), they performed only at certain stages of the World Rally Championship (New Zealand, Great Britain, Greece, Sweden), which were primarily of interest to the marketing departments of concerns. There were enough national titles: for example, in 1975-1980. Rod Millen won as many as five in New Zealand and the USA. But in the WRC, the successes were exclusively local: the best that the RX-7 showed was 3rd and 6th places in the Greek Acropolis in 1985.

Well, the loudest success of Mazda in general and RPD in particular was the victory of its sports prototype 787B (2612 cm3, 700 hp, 607 Nm, 377 km/h) at Le Mans in 1991. Moreover, it was not only fast pilots and competitive equipment that helped to overcome the factory Porsches, Peugeot and Jaguars: the perseverance of Japanese managers also played a role, regularly “knocking out” all sorts of relaxations in the regulations for rotors. So, on the eve of the victory of the 787th, the organizers of the race agreed to compensate for the voracity of the “rotors” with a 170-kilogram (830 versus 1000) weight reduction. The paradox was that, unlike gasoline engines, the "appetite" of the RPD with further forcing grew at a much more modest pace than that of conventional piston engines, and the 787th turned out to be more economical than its main competitors!

It was a shock. Mercedes, which Stern magazine for its conservatism called nothing more than “a car manufacturer for 50-year-old gentlemen in hats,” presented a supercar in 1969 that even struck the imagination in color. The defiant bright orange color, emphatically wedge-shaped shape, mid-engine layout, gull-wing doors and a heavy-duty three-section RPD (3600 cm3, 280 hp, 260 km / h) - for a conservative Mercedes it was something!

And since the company did not build concepts, everyone believed that the C111 had only one way: a small-scale (homologation) assembly and a great racing future, because since 1966 the FIA allowed the RPD to official competitions. And checks rained down at the headquarters of Mercedes with a request to enter the right amount for the right to possess C111. The Stuttgarters, on the other hand, further fueled interest in the Eske, in 1970 introducing the second generation of the coupe with an even more fantastic design, a 4-section rotor and mind-blowing performance (4800 cm3, 350 hp, 300 km / h). To fine-tune, Mercedes built five mock-ups that spent days and nights at the Hockenheimring and Nurburgring, preparing to set a series of speed records. The press relished the upcoming "clash of the titans" between the rotary Mercedes, the naturally aspirated Ferrari and the supercharged Porsche in the World Endurance Championship. Alas, the return to big sport did not take place. Firstly, C111 was very expensive even for Mercedes, Secondly, the Germans could not put such a crude design on sale. And after the Caribbean oil crisis, they generally covered the project, focusing on diesel engines. They were equipped latest versions C111, who set several world records.

Having no completed technical education, at the end of his life, Felix Wankel achieved world recognition in the field of engine building and sealing technology, having won a lot of awards and titles. The streets and squares of German cities (Felix-Wankel-Strasse, Felix-Wankel-Ring) are named after him. In addition to engines, Wankel developed a new concept for high-speed craft and built several boats himself.

The most interesting thing is that the rotary engine, which made him a millionaire and brought him worldwide fame, Wankel did not like, considering him an "ugly duckling." Real working RPDs were made according to the so-called "KKM concept", which provides for planetary rotation of the rotor and requires the introduction of external counterweights. A significant role was played by the fact that this scheme was proposed not by Wankel, but by NSU engineer Walter Freude. Wankel himself last days considered the ideal engine layout “with rotating pistons without unevenly rotating parts” (Drehkolbenmasine - DKM), conceptually much more beautiful, but technically complex, requiring, in particular, the installation of spark plugs on a rotating rotor. Nevertheless, rotary engines all over the world are associated precisely with the name of Wankel, since everyone who knew the inventor closely unanimously claims that without the irrepressible energy of the German engineer, the world would not have seen this amazing device. Felik Wankel passed away in 1988.
The history of the Mercedes 350 SL is curious. Wankel really wanted to have a rotary Mercedes C-111. But Mercedes did not go towards him. Then the inventor took the serial 350 SL, threw out the “native” engine from there and installed a rotor from the C-111, which was 60 kg lighter than the previous 8-cylinder, but developed significantly more power (320 hp at 6500 rpm). In 1972, when the engineering genius finished work on his next miracle, he could have been behind the wheel of the fastest Mercedes SL-class at that time. The irony was that Wankel never got a driver's license for the rest of his life.

Specially for new engine was developed Mazda car RX-8, which, according to the brand manager Mazda Motor Europe Martin Brink, was created according to a new concept - the car was "built" around the engine. As a result, the weight distribution along the axes of the RX-8 is ideal - 50 to 50. The use of a unique shape and small dimensions of the engine made it possible to place the center of gravity very low. “The RX-8 is not a racing monster, but it is the best handling car I have ever driven,” Martin Brink enthused Popular Mechanics.

Barrel of honey...

Without a doubt, at first glance, a rotary piston engine has a lot of advantages over traditional engines internal combustion:
- 30-40% fewer parts;
- Smaller in 2-3 times dimensions and weight, in comparison with the standard internal combustion engine corresponding in power;
- Smooth torque response over the entire rpm range;
- Absence of a crank mechanism, and, consequently, a much lower level of vibration and noise;
- High level revolutions (up to 15000 rpm!).

A spoon of tar…

It would seem that if the Wankel has such advantages over the piston engine, then who needs these bulky, heavy, rattling and vibrating piston engines? But, as is often the case, in practice, everything is far from so chocolate. None brilliant invention, leaving the threshold of the laboratory, was sent to the basket marked "for waste." Mass production found not on one stone, but on a whole placer of granite:
- Development of the combustion process in a chamber of unfavorable shape;
- Ensuring tightness of seals;
- Ensuring work without warpage of the body in conditions of uneven heating;
- Low thermal efficiency due to the fact that the RPD combustion chamber is much larger than that of a traditional internal combustion engine;
- high consumption fuel;
- High toxicity of gaseous products of combustion;
- Narrow temperature zone for RPD operation: at low temperatures engine power drops sharply, at high - rapid wear of the rotor seals.

And what else? Pluses or minuses? Is the game worth the candle? Does it make sense (if not more - the possibility) to master the mass production of RPDs?

The main difference between the internal structure and the principle of operation of a rotary engine from an internal combustion engine is the complete absence of motor activity, while it is possible to achieve high engine speeds. The rotary engine, or otherwise the Wankel engine, has a number of other advantages, which we will consider in more detail.

The general principle of the design of a rotary engine

The RPD is clad in an oval body for optimal placement of the triangular rotor. Distinctive feature rotor in the absence of connecting rods and shafts, which greatly simplifies the design. In fact, the key parts of the RD are the rotor and stator. The main motor function in this type of motor is carried out due to the movement of the rotor located inside the housing, which is similar to an oval.

The principle of operation is based on the high-speed movement of the rotor in a circle, as a result, cavities are created to start the device.

Why are rotary engines not in demand?

The paradox of a rotary engine lies in the fact that, for all its simplicity of design, it is not as in demand as an internal combustion engine, which has very complex design features and difficulties in carrying out repair work.

Of course, the rotary engine is not without drawbacks, otherwise it would have found wide application in the modern automotive industry, and perhaps we would not have known about the existence of internal combustion engines, because the rotary engine was designed much earlier. So why complicate the design so much, let's try to figure it out.

Obvious shortcomings rotary motor can be considered the lack of reliable sealing in the combustion chamber. This is easily explained by the design features and operating conditions of the motor. In the course of intense friction of the rotor with the cylinder walls, uneven heating of the body occurs and, as a result, the metal of the body expands from heating only partially, which leads to pronounced violations of the sealing of the body.

To enhance the sealing properties, especially if there is a pronounced difference temperature conditions between the chamber and the intake or exhaust system, the cylinder itself is made of different metals and placed in different parts of the cylinder to improve tightness.

To start the motor, only two candles are used, this is due to the design features of the motor, which make it possible to produce 20% more efficiency, in comparison with an internal combustion engine, for the same period of time.

Zheltyshev rotary engine - principle of operation:

Benefits of a rotary engine

With small dimensions, it is capable of developing high speed, but there is a big minus in this nuance. Despite its small size, it is the rotary engine that consumes a huge amount of fuel, but the engine's service life is only 65,000 km. So, an engine of only 1.3 liters consumes up to 20 liters. fuel per 100 km. Perhaps this was the main reason for the lack of popularity of this type of motor for mass consumption.

The price of gasoline has always been considered an urgent problem of mankind, given that the world's oil reserves are located in the Middle East, in a zone of constant military conflicts, gasoline prices remain quite high, and in the short term there are no trends to reduce them. This leads to the search for solutions for the minimum consumption of resources without sacrificing power, which is the main argument in favor of the internal combustion engine.

All this together has determined the position of rotary engines as a suitable option for sports cars. However, the world-famous car manufacturer Mazda continued the work of the inventor Wankel. Japanese engineers are always trying to extract the maximum benefit from unclaimed models by modernizing and applying innovative technologies, which allows them to maintain their leading positions in the global automotive market.

The principle of operation of the Akhriev rotary engine in the video:

The new Mazda model, equipped with a rotary engine, is as powerful as the advanced German models, delivering up to 350 horsepower. At the same time, fuel consumption was incomparably high. Mazda design engineers had to reduce the power to 200 horsepower, which made it possible to normalize fuel consumption, but the compact size of the engine made it possible to give the car additional advantages and compete with European car models.

In our country, rotary engines have not taken root. There were attempts to install them on the transport of specialized services, but this project was not funded in the proper amount. Therefore, all successful developments in this direction belong to Japanese engineers from the Mazda company, which intends to soon show a new car model with a modernized engine.

How a Wankel rotary motor works on video

The principle of operation of a rotary engine

The RPD works by rotating the rotor, so power is transferred to the gearbox through the clutch. The transforming moment consists in the transfer of fuel energy to the wheels due to the rotation of the rotor made of alloy steel.

The mechanism of operation of a rotary piston engine:

fuel compression;
fuel injection;
oxygen enrichment;
combustion of the mixture;
release of fuel combustion products.

How a rotary engine works is shown in the video:

The rotor is fixed on a special device; during rotation, it forms cavities independent of each other. The first chamber is filled with an air-fuel mixture. Subsequently, it is thoroughly mixed.

Then the mixture passes into another chamber, where compression and ignition takes place, thanks to the presence of two candles. Subsequently, the mixture moves to the next chamber, parts of the processed fuel that exit the system are displaced from it.

This is how a complete cycle of operation of a rotary piston engine occurs, based on three cycles of work in just one revolution of the rotor. It was the Japanese developers who managed to significantly modernize the rotary engine and install three rotors in it at once, which can significantly increase power.

The principle of operation of the Zuev rotary engine:

Today, the advanced two-rotor engine is comparable to a six-cylinder internal combustion engine, and the three-rotor engine is not inferior in power to 12 cylinder engine internal combustion.

Do not forget about the compact size of the engine and the simplicity of the device, which allows, if necessary, to carry out repairs or complete replacement main motor units. Thus, Mazda engineers managed to give a second life to this simple and productive device.

The principle of operation of the RPD is based on the expansion pressure of gases, which is created during the combustion of fuel. The main difference and positive moment of RPD is the absence of masses with reciprocating movements. All movement of parts occurs in a circle without sudden stops. In a conventional piston internal combustion engine, the piston and connecting rod come to a complete stop at the top and bottom. dead spots, which creates significant inertial forces and requires the use of high-strength materials.

The main part of the design is the rotor, which turns pressure into a circular motion. The rotor in the simplest case has the shape of a triangle with convex edges (the so-called Reuleaux triangle) and is / rotates in an oval housing of a special profile, the surface of which is made according to the epitrochoid (options with a different shape of the rotor and housing are possible). In the cavities between the rotor and the housing, completely isolated friend from each other and changing their volume during the rotation of the rotor, a number of processes (cycles) occur - air supply, fuel injection, mixture compression, creation of a spark, exhaust gas exhaust:

the air-fuel mixture enters and mixes into the first cavity through the inlet window (the opening and closing of the window is performed by the edge of the rotor, similar to a two-stroke piston engine);
the rotor moves the resulting substance into the second cavity, where compression and ignition take place;
in the third cavity, the mixture expands and the exhaust gases are removed through the outlet window (it also opens and closes with the edge of the rotor).

The key point is that these processes do not occur sequentially, but simultaneously and in parallel, i.e. for one revolution of the rotor, all three cycles occur.

The rotation of the rotor occurs on an eccentric - a pair of gears, the largest of which is located on the inner surface of the rotor, and the smaller, supporting one, is rigidly attached to the inner surface of the engine side cover. The rotational motion of the rotor is transmitted to an eccentric shaft mounted on bearings and transmitting torque to the transmission mechanisms. Thus, two mechanical pairs work simultaneously in the RPD: the first one regulates the movement of the rotor and consists of a pair of gears; and the second - converting the circular motion of the rotor into rotation of the eccentric shaft. The gear ratio of the rotor and stator gears is 2:3, so for one complete revolution of the eccentric shaft, the rotor has time to turn 120 degrees. In turn, for one complete revolution of the rotor in each of the three chambers formed by its faces, a complete four-stroke cycle of the internal combustion engine is performed.

To ensure balance (especially on idling) requires a minimum of two rotors, although a single rotor design is also used. Mazda engines have up to three rotors (sections).

The overall efficiency of the Wankel rotary engine (thermal and mechanical efficiency) is about 40-45%. For comparison, conventional piston internal combustion engines have 25% efficiency (according to other sources - 34%), and modern turbodiesels up to 40% (according to other sources - 50%).

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Classification of rotary internal combustion engines

To uncover...

The classification of rotary engines occurs according to the type of operation of the combustion chamber - it is hermetically sealed for a while, or has a constant connection with the atmosphere. The latter type includes gas turbines, the combustion chambers of which are separated from the exhaust nozzle (from the atmosphere) only by a thick "palisade" of the rotor impeller blades.

Rotary internal combustion engines with hermetically sealed combustion chambers are divided into 7 different structural layouts:

Rotary engines with non-uniform multidirectional (reciprocating-rotational) movement of the main working element. The rotor does not rotate here, but, as it were, swings around its axis. The compression process takes place between the motor blades.
Rotary engines with uneven unidirectional (pulsating-rotational) movement of the main working element. There are two rotors inside the case. Compression passes between the vanes of these two elements as they approach and recede.
Rotary motors with a simple and uniform rotational movement of the main working element and with sealing flaps-blades moving in the rotor. This design is still widely used in pneumatic motors. For rotary internal combustion engines, the chamber in which the ignition takes place is significantly altered.
A special case - with dampers-blades deviating on hinges on the rotor.
Rotary motors with a simple and uniform rotational movement of the main working element and with sealing flaps moving in the housing.
Rotary motors with a simple and uniform rotational movement of the main working element and using the same simple rotational movement of the sealing elements.
Rotary motors with a simple rotational movement of the main working element, without the use of separate sealing elements and a spiral organization of the shape of the working chambers. They are considered the most technically advanced due to the absence of parts that perform reciprocating translational movements. They are the RPD (“Wankel engine”) in the classical modern sense. RPDs of this type easily reach 10,000 rpm.
Rotary motors with planetary rotational movement of the main working element and without the use of separate sealing elements. The very first modification invented by Freude and Wankel.

Advantages of RPD

To uncover...

The design of the RPD is relatively small (1.5-2 times less than a classic ICE of the same power) and has a low weight, which improves the controllability of the machine, facilitates the optimal location of the transmission (weight distribution) and frees up more internal layout space.
Due to the lack of conversion of reciprocating motion into rotational and the associated inertia forces, the RPD can withstand much higher speeds compared to traditional engines. As a result - excellent dynamic qualities (high power density - a 1.3-liter engine produces 220 hp, and with a turbocharger - 350 hp!), high maximum speed (up to 10,000 rpm), excellent throttle response and a flat torque curve.
Power output from each section during 3/4 revolution of the output shaft (single-piston internal combustion engine produces power only 1/4 revolution).
Minimum vibration, excellent balance (especially in twin-rotor engines).
35-40% fewer parts in the design in general and moving masses in particular (there are no pistons, connecting rods, crankshaft, in the "classic version" - a gas distribution mechanism), a much smaller mass of moving parts.
In the simplest version of the RPD, there is no separate lubrication system - oil is added to the fuel, as in the operation of two-stroke motorcycle engines. The lubrication of friction pairs (primarily the rotor and the working surface of the combustion chamber) in this embodiment is carried out by the fuel-air mixture itself.

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Disadvantages of RPD

To uncover...

Low efficiency of gap seals between the rotor and the combustion chamber. The RPD rotor, which has a complex shape, requires reliable seals not only along the edges (and there are four of them on each surface - two along the top, two along the side faces), but also along the side surface in contact with the engine covers. In this case, the seals are made in the form of spring-loaded strips of high-alloy steel with particularly precise processing of both working surfaces and ends. The allowances for expansion of the metal from heating impair their characteristics - it is almost impossible to avoid gas breakthrough at the end sections of the sealing plates (in piston engines, the labyrinth effect is used by installing sealing rings with gaps in different directions).
The complex sealing system of the rotor requires sophisticated and efficient lubrication of the friction surfaces. RPD consumes more oil than a four-stroke piston engine (from 400-1200 ml per 1000 km, replacement every 5000 km). RPD owners recommend checking the oil level every morning. In this case, the oil burns along with the fuel, which sharply worsens the ecology of the RPD.
Special requirements for oil quality - due to the tendency to increased wear (due to the large area of \u200b\u200bcontacting parts - the rotor and the inner chamber of the engine) and overheating (due to increased friction and the small size of the engine itself). For RPDs, irregular oil changes are deadly (abrasive particles in old oil dramatically increase wear) and engine hypothermia. Starting a cold engine and insufficient warming up lead to the fact that there is little lubrication in the contact zone of the rotor seals with the surface of the combustion chamber and side covers. If a piston engine most often jams when overheating, then RPD - during a cold engine start or operation in cold weather when cooling is excessive.
High fuel consumption for low revs(and generally speaking). Theoretically, it can be eliminated by turning off part of the sections at low speeds, which at the same time reduces the temperature load.
High demands on the geometric accuracy of parts manufacturing and, as a result, high complexity of production. The use of high-tech and high-precision equipment is required: machines capable of moving the tool along a complex trajectory of the epitrochoidal surface of the volumetric displacement chamber.
The connection of the rotor with the output shaft through an eccentric mechanism ( salient feature RPD Wankel) causes pressure between the rubbing surfaces, which, combined with high temperatures, leads to additional wear and heating of the engine.
High pressure drops between the rotor chambers with a very small contact patch area. As a result, rapid wear of seals and very high requirements for them, in general, a short engine life (the key problem of RPD is high leakage between chambers, a drop in efficiency and an increase in exhaust toxicity). So, for the Mazda RX-8, the engine life is about 100-150 thousand kilometers with proper and timely maintenance, after which a major overhaul is carried out with the replacement of seals. Partially, the problem of rapid wear of seals at high shaft speeds was solved by using high-alloy steel.
Less elasticity relative to classic piston ICEs - RPD gives out optimal power only at high speeds, which requires the complexity of the transmission.
Poor geometry of the combustion chamber, which in RPD has a lenticular shape, i.e. relatively large area with a small volume. During combustion of the working mixture, the main energy losses go through radiation, so the ideal shape of the combustion chamber is spherical. Heat losses not only reduce the efficiency of converting chemical energy into mechanical energy, but also lead to severe engine overheating (i.e. higher thermal conditions), as well as poor combustion fuel-air mixture and prone to detonation. Partially, this problem is solved by installing two candles in different zones on one combustion chamber.
Small resource of spark plugs, their overheating, the need to replace every 10,000 km.

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RPD device

To uncover...

The rotor mounted on the shaft is rigidly connected to the gear wheel, which engages with the fixed gear - the stator. The diameter of the rotor is much larger than the diameter of the stator, despite this, the rotor with the gear wheel rolls around the gear. Each of the tops of the trihedral rotor moves along the epitrochoidal surface of the cylinder and cuts off the variable volumes of the chambers in the cylinder using three valves.

This design allows any 4-stroke Diesel, Stirling or Otto cycle to be carried out without the use of a special gas distribution mechanism. The sealing of the chambers is provided by radial and end sealing plates pressed against the cylinder by centrifugal forces, gas pressure and band springs. The absence of a gas distribution mechanism makes the engine much simpler than a four-stroke piston engine, and the absence of interface (crankcase space, crankshaft and connecting rods) between individual working chambers ensures extraordinary compactness and high power density. For one revolution of the eccentric shaft, the engine performs one work cycle, which is equivalent to the operation of a two-cylinder piston engine. In one revolution of the rotor, the eccentric shaft performs 3 revolutions and 9 working strokes, which leads to erroneous comparisons between a rotary engine and a six-cylinder piston engine.

The mixture formation, ignition, lubrication, cooling, start-up are fundamentally the same as in a conventional piston internal combustion engine.

Practical application was received by engines with trihedral rotors, with the ratio of gear and gear radii: R: r = 2: 3, which are installed on cars, boats, etc.

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Application

To uncover...

First stock car with a rotary engine became the NSU Spider, which was released in 1964. NSU- German company, founded in 1873, which produced cars and motorcycles. Until 1969, it existed as separate company, then was bought by the Volkswagen Group.

The first mass model (37204 copies) was the NSU Ro-80 model, a real breakthrough thanks to the right marketing. However, relying on the "revolutionary technology" of the RPD, which has not yet been debugged in real conditions, has become a serious mistake. The engine resource was no more than 50 thousand kilometers, and often much less. The RPD was often replaced with a Ford L4 "Essex" piston.

RPDs were also installed on cars:

Citroen GS Birotor (Citroën M35 project)
Mercedes-Benz С111
Chevrolet Corvette
VAZ 21018 (1976), 21079 and 2110 (modifications for special services)
Mazda (since 1978, Cosmo Sport and Rotor-eXperiment series commonly known as RX)

The RX series ended in 2008 with the RX-8 model. In total, more than a million cars with RPD were produced in the series. In total, at the peak of its popularity, the patent for the Wankel engine was bought by 11 of the world's leading automakers.

Interestingly, Mazda cars with the letters RE in the name (the first letters of the name "Renesis") can use both gasoline and hydrogen as fuel (because it is less sensitive to detonation than a conventional engine using a reciprocating piston).

RPDs are also used on motorcycles (in small series) and in aviation modeling.

Interestingly, having received a patent for RPD in 1936, Felix Wankel became the inventor of not only the internal combustion engine, but also the rotary piston pump and compressor. And these devices can be found much more often than RPDs - in production, in repair shops, in everyday life. For example, portable electric compressors for motorists are very often arranged on the principle of a rotary piston pump.

Steam engines and internal combustion engines have one common drawback - the reciprocating movement of the piston must be converted into rotational movement of the wheels. Hence the obviously low efficiency and high wear of the mechanism elements. Many wanted to build an internal combustion engine so that all moving parts in it only rotated - as happens in electric motors.

However, the task turned out to be not easy, only a self-taught mechanic, who in his entire life never received a higher education, or even a working specialty, managed to successfully solve it.

Felix Heinrich Wankel (1902–1988) was born on August 13, 1902 in the small German town of Lahr. During the First World War, Felix's father died, because of which the future inventor had to leave the gymnasium and go to work as an apprentice seller in a bookstore at a publishing house. Through this work, Wankel became addicted to reading books, from which he independently studied technical disciplines, mechanics and automotive engineering.
There is a legend that the solution to the problem came to the seventeen-year-old Felix in a dream. Whether this is true or not is unknown. But it is obvious that Felix had a very outstanding ability to mechanics and a "non-soapy" look at things. He understood how all four cycles of a conventional internal combustion engine (injection, compression, combustion, exhaust) can be carried out while rotating.
Quite quickly, Wankel came up with the first engine design, and in 1924 he organized a small workshop, which also served as an impromptu "laboratory". Here Felix began to conduct the first serious research in the field of rotary piston internal combustion engines.
From 1921, Wankel was an active member of the NSDAP. He advocated party ideals, was the founder of the All-German Military Youth Association and the Jungführer of various organizations. In 1932, he left the party after accusing one of his former colleagues of political corruption. However, on a counter-charge, he himself had to spend six months in prison. Released from prison thanks to the intercession of Wilhelm Keppler, he continued to work on the engine. In 1934 he created the first prototype and received a patent for it. He designed new valves and combustion chambers for his motor, created several different versions of it, developed a classification of kinematic schemes for various rotary piston machines.

In 1936, BMW became interested in the Wankel engine prototype - Felix received money and his own laboratory in Lindau to develop experimental aircraft engines.
However, until the very defeat of Nazi Germany, not a single Wankel engine went into production. Perhaps it took too much time to bring the design to mind and create mass production.
After the war, the laboratory was closed, the equipment was taken to France, and Felix was left without a job (his former membership in the National Socialist Party affected him). However, Wankel soon got a position as a design engineer at NSU Motorenwerke AG, one of the oldest manufacturers of motorcycles and cars.
In 1957, by the joint efforts of Felix Wankel and NSU lead engineer Walter Froede, a rotary piston engine was first installed on the NSU Prinz car. The initial design turned out to be far from perfect: even to replace the candles, it was necessary to disassemble almost the entire “engine”, reliability left much to be desired, and it was a sin to talk about efficiency at this stage of development. As a result of the tests, a car with a traditional internal combustion engine went into the series. Nevertheless, the first rotary-piston engine DKM-54 proved its fundamental performance, opened up directions for further refinement and demonstrated the colossal potential of the “rotors”.
Thus, a new type of internal combustion engine finally got its start in life. In the future, it will have many more improvements and improvements. But the prospects for a rotary piston engine are so attractive that nothing could stop engineers from bringing the design to operational excellence.

Before analyzing the advantages and disadvantages of rotary piston internal combustion engines, it is still worth considering their design in more detail.
A round hole was made in the center of the rotor, covered from the inside with teeth like a gear. A rotating shaft of smaller diameter, also with teeth, is inserted into this hole, which ensures that there is no slippage between it and the rotor. The ratios of the diameters of the hole and the shaft are chosen so that the vertices of the triangle move along the same closed curve, which is called the "epitrochoid" - Wankel's art as an engineer was to first understand that this was possible, and then calculate everything exactly. As a result, the piston, which has the shape of a Reuleaux triangle, cuts off in the chamber, repeating the shape of the curve found by Wankel, three chambers of variable volume and position.
The design of a rotary piston internal combustion engine allows you to implement any four-stroke cycle without the use of a special gas distribution mechanism. Thanks to this fact, the "rotor" turns out to be much simpler than a conventional four-stroke piston engine, in which, on average, there are almost a thousand more parts.
The sealing of the working chambers in a rotary-piston internal combustion engine is provided by radial and end sealing plates pressed against the "cylinder" by tape springs, as well as by centrifugal forces and gas pressure.
Another of its technical features is its high “labor productivity”. For one complete revolution of the rotor (that is, for the cycle "injection, compression, ignition, exhaust"), the output shaft makes three complete revolutions. In a conventional piston engine, such results can only be achieved using a six-cylinder internal combustion engine.

After the first successful demonstration of a rotary internal combustion engine in 1957, the largest auto giants began to show increased interest in the development. At first, the license for the engine, which received the informal name "Wankel", was bought by Curtiss-Wright Corporation, a year later, Daimler-Benz, MAN, Friedrich Krupp and Mazda. In just a very short period of time, licenses for the new technology were acquired by about a hundred companies around the world, including such monsters as Rolls-Royce, Porsche, BMW and Ford. - in a rotary piston engine, there are 40% fewer parts, it is easier to repair and manufacture.

The picture is clickable:

The rotary piston engine develops high power with a rather modest fuel consumption. For example, a modern “wankel” with a volume of only 1300 cm3 develops a power of 220 hp, and with a turbocharger - all 350. Another example is the miniature OSMG 1400 engine weighing 335 g (5 cm3 working volume) develops a power of 1.27 liters .With. In fact, this little one is 27% stronger than a horse.
Another important advantage is the low level of noise and vibration. The rotary piston engine is perfectly balanced mechanically, in addition, the mass of moving parts (and their number) in it is much less, so that the "Wankel" runs much quieter and does not vibrate.
And finally, the rotary piston engine has excellent dynamic characteristics. In low gear, you can accelerate the car to 100 km / h at high engine speeds without much load on the engine. In addition, the Wankel design itself, due to the lack of a mechanism for converting reciprocating motion into rotational motion, is able to withstand higher speeds than a traditional internal combustion engine.

After the NSU Spyder released in 1964, the legendary NSU Ro 80 model followed (there are still many clubs of owners of these cars in the world), Citroen M35 (1970), Mercedes C-111 (1969), Corvette XP (1973). But the only mass manufacturer was the Japanese Mazda, which has been producing since 1967, sometimes 2-3 new models with RPD. Rotary engines were put on boats, snowmobiles and light aircraft. The end of euphoria came in 1973, at the height of the oil crisis. It was then that the main drawback of rotary engines appeared - inefficiency. With the exception of Mazda, all automakers ended rotary programs, and the Japanese company's sales in America declined from 104,960 cars sold in 1973 to 61,192 in 1974. Along with undeniable advantages, the Wankel also had a number of very serious drawbacks. First, durability. One of the first prototypes of rotary-piston engines ran out of service in just two hours. The next, more successful DKM-54 had already endured a hundred hours, but this was still not enough for the normal operation of the car. The main problem lay in the uneven wear of the inner surface of the working chamber. During operation, transverse furrows appeared on it, which received the speaking name "devil's marks".

At Mazda, after acquiring a license for the Wankel, a whole department was formed to improve the rotary piston engine. Pretty soon it turned out that when the triangular rotor rotates, the plugs on its tops begin to vibrate, as a result of which “devil marks” are formed.
At present, the problem of reliability and durability has been finally solved by using high-quality wear-resistant coatings, including ceramic ones.
Another serious problem is the increased toxicity of the Wankel exhaust. Compared to a conventional reciprocating internal combustion engine, a “rotornik” emits less nitrogen oxides into the atmosphere, but much more hydrocarbons, due to incomplete combustion of fuel. Quite quickly, Mazda engineers, who believed in the bright future of the Wankel, found a simple and effective solution to this problem. They created the so-called thermal reactor, in which the hydrocarbon residues in the exhaust gases were simply “burned out”. The first car to implement this scheme was the Mazda R100, also called the Familia Presto Rotary, released in 1968. This car, one of the few, immediately passed the very stringent environmental requirements put forward by the United States in 1970 for imported cars.
The next problem of rotary piston engines partially follows from the previous one. This is economy. The fuel consumption of a standard "wankel" due to incomplete combustion of the mixture is significantly higher than that of a standard internal combustion engine. Once again, Mazda engineers set to work. Through a series of measures, including redesigning the thermoreactor and carburetor, adding a heat exchanger to the exhaust system, developing a catalytic converter, and introducing a new ignition system, the company has achieved a 40% reduction in fuel consumption. As a result of this undeniable success, the Mazda RX-7 sports car was released in 1978.

It is worth noting that at that time only Mazda and ... AvtoVAZ produced cars with rotary piston engines all over the world.
It was in the disastrous year of 1974 that the Soviet government created a special design bureau RPD (SKB RPD) at the Volga Automobile Plant - the socialist economy is unpredictable. In Togliatti, work began on the construction of workshops for the mass production of "wankels". Since the VAZ was originally planned as a simple copyer of Western technologies (in particular, Fiat ones), the factory specialists decided to reproduce the Mazda engine, completely discarding all the ten-year developments of domestic engine-building institutes.
Soviet officials negotiated with Felix Wankel for quite some time regarding the purchase of licenses, some of which took place right in Moscow. True, no money was found, and therefore it was not possible to use some proprietary technologies. In 1976, the first Volga single-section VAZ-311 engine with a capacity of 65 hp was put into operation, it took another five years to fine-tune the design, after which an experimental batch of 50 units of VAZ-21018 rotary "units" was produced, which instantly dispersed among VAZ workers. It immediately became clear that the engine only outwardly resembled a Japanese one - it began to crumble in a very Soviet way. The management of the plant was forced to replace all engines with serial piston engines in six months, cut the staff of SKB RPD by half and suspend the construction of workshops. The salvation of the domestic rotary engine building came from the special services: they were not very interested in fuel consumption and engine life, but they were very interested in dynamic characteristics. Immediately, a two-section RPD with a power of 120 hp was made from two VAZ-311 engines, which began to be installed on a “special unit” - VAZ-21019. It is this model, which received the unofficial name "Arkan", that we owe countless tales about police "Cossacks" catching up with fancy "Mercedes", and many law enforcement officers - orders and medals. Until the 90s, the outwardly unpretentious Arkan really easily overtook all cars. In addition to VAZ-21019, AvtoVAZ also produces small batches of VAZ-2105, -2107, -2108, -2109, -21099 cars. The maximum speed of the rotary "eight" is about 210 km / h, and it accelerates to hundreds in just 8 seconds.
Revived on special orders, SKB RPD began to make engines for water sports and motorsport, where cars with rotary engines began to win prizes so often that sports officials were forced to ban the use of RPD.
In 1987, the head of the SKB RPD, Boris Pospelov, died, and Vladimir Shnyakin, a man who came to the automotive industry from aviation and dislikes ground transport, was elected at a general meeting. The main direction of SKB RPD is the creation of engines for aviation. This was the first strategic mistake: we produce disproportionately fewer cars, and the plant lives from the sold engines.
The second mistake was the orientation in the preserved production of automotive RPDs to low-power VAZ-1185 engines of 42 hp. for the Oka, although more voracious, but more dynamic rotary engines are asking for the fastest domestic cars - for example, for the G8. The same Japanese install "wankels" only on sports models. As a result, there were only a few rotary minicars "Oka" on Russian roads. In 1998, a civilian version of the two-cylinder rotary 1.3-liter VAZ-415 engine was finally prepared, which was installed on the VAZ-2105, 2107, 2108 and 2109.

At present, only Mazda is engaged in serious research in the field of rotary piston engines, gradually improving their design, and most of the pitfalls in this area have already been overcome. "Wankels" are quite consistent with world standards in terms of exhaust toxicity, fuel consumption and reliability. For modern machine tools, the surfaces described by the epitrochoid are not a problem (just as much more complex curves are not a problem), new structural materials make it possible to increase the service life of a rotary piston engine, and its cost is already lower than that of a standard internal combustion engine due to fewer used details.
Like NSU, Mazda in the 60s. was a small company with limited technical and financial resources. The basis of its lineup was delivery trucks and family runabouts. Therefore, it is not surprising that the Mazda 110S Cosmo sports coupe (982 cm3, 110 hp, 185 km/h) was created for more than 6 years and turned out to be very capricious and expensive. And the damaged reputation of the NSU Ro80 did not contribute to the excitement (in 1967-1972 only 1175 "spaces" found their owners), but the world interest in the 110S contributed to an increase in sales of all the rest of the company's products!
To prove that the RPD is just as reliable (its superiority in power has already become obvious to everyone), Mazda took part in the competition for almost the first time in its life, and chose the most difficult and longest race - the 84-hour Marathon De La Route, held on Nurburgring. How the crew from Belgium managed to take 4th place (the second car retired three hours before the finish line due to jammed brakes), losing only to the Porsche 911 “grown up” on the Nordschleife, seems to remain a mystery.

Wankel workshop in Lindau

Although since then the Japanese “rotorniks” have become regulars on the race tracks, they had to wait 16 years for a major success in Europe. In 1984, the British won the prestigious Spa-Francochamps daily race with an RX-7. But in the USA, in the main market of the "seven", her racing career developed much more successfully: from the moment she made her debut in the IMSA GT championship in 1978 and until 1992, she won more than a hundred stages in her class, and from 1982 to 1992 she won more than a hundred stages. excelled in the main race of the series - 24 hours of Daytona.
In the rally, the Mazda did not go so smoothly. As was often the case with Japanese teams (Toyota, Datsun, Mitsubishi), they performed only at certain stages of the World Rally Championship (New Zealand, Great Britain, Greece, Sweden), which were primarily of interest to the marketing departments of concerns. There were enough national titles: for example, in 1975-1980. Rod Millen won as many as five in New Zealand and the USA. But in the WRC, the successes were exclusively local: the best that the RX-7 showed was 3rd and 6th places in the Greek Acropolis in 1985.
Well, the loudest success of Mazda in general and RPD in particular was the victory of its sports prototype 787B (2612 cm3, 700 hp, 607 Nm, 377 km/h) at Le Mans in 1991. Moreover, it was not only fast pilots and competitive equipment that helped to overcome the factory Porsches, Peugeot and Jaguars: the perseverance of Japanese managers also played a role, regularly “knocking out” all sorts of relaxations in the regulations for rotors. So, on the eve of the victory of the 787th, the organizers of the race agreed to compensate for the voracity of the “rotors” with a 170-kilogram (830 versus 1000) weight reduction. The paradox was that, unlike gasoline engines, the "appetite" of the RPD with further forcing grew at a much more modest pace than that of conventional piston engines, and the 787th turned out to be more economical than its main competitors!

And since the company did not build concepts, everyone believed that the C111 had only one way: a small-scale (homologation) assembly and a great racing future, because since 1966 the FIA allowed the RPD to official competitions. And checks rained down at Mercedes headquarters asking them to enter the required amount for the right to own the C111. The Stuttgarters, on the other hand, further fueled interest in the Eske, in 1970 introducing the second generation of the coupe with an even more fantastic design, a 4-section rotor and mind-blowing performance (4800 cm3, 350 hp, 300 km / h). To fine-tune, Mercedes built five mock-ups that spent days and nights at the Hockenheimring and Nurburgring, preparing to set a series of speed records. The press relished the upcoming "clash of the titans" between the rotary Mercedes, the naturally aspirated Ferrari and the supercharged Porsche in the World Endurance Championship. Alas, the return to big sport did not take place. Firstly, the C111 was very expensive even for Mercedes, and secondly, the Germans could not sell such a crude design. And after the Caribbean oil crisis, they generally covered the project, focusing on diesel engines. They equipped the latest versions of the C111, which set several world records.

The most interesting thing is that the rotary engine, which made him a millionaire and brought him worldwide fame, Wankel did not like, considering him an "ugly duckling." Real working RPDs were made according to the so-called "KKM concept", which provides for planetary rotation of the rotor and requires the introduction of external counterweights. A significant role was played by the fact that this scheme was proposed not by Wankel, but by NSU engineer Walter Freude. Until recently, Wankel himself considered the ideal engine layout “with rotating pistons without unevenly rotating parts” (Drehkolbenmasine - DKM), conceptually much more beautiful, but technically complex, requiring, in particular, the installation of spark plugs on a rotating rotor. Nevertheless, rotary engines all over the world are associated precisely with the name of Wankel, since everyone who knew the inventor closely unanimously claims that without the irrepressible energy of the German engineer, the world would not have seen this amazing device. Felik Wankel passed away in 1988.
The history of the Mercedes 350 SL is curious. Wankel really wanted to have a rotary Mercedes C-111. But the company Mercedes did not go to meet him. Then the inventor took the serial 350 SL, threw out the “native” engine from there and installed a rotor from the C-111, which was 60 kg lighter than the previous 8-cylinder, but developed significantly more power (320 hp at 6500 rpm). In 1972, when the engineering genius finished work on his next miracle, he could have been behind the wheel of the fastest Mercedes SL-class at that time. The irony was that Wankel never got a driver's license for the rest of his life.

We owe the revival of interest in RPD to the new Mazda Renesis engine (from RE - Rotary Engine - and Genesis). Over the past decade, Japanese engineers have managed to solve all the main problems of RPD - exhaust toxicity and inefficiency. Compared to its predecessor, it was possible to reduce oil consumption by 50%, gasoline by 40% and bring the emission of harmful oxides to Euro IV standards. A two-cylinder engine with a volume of only 1.3 liters produces 250 hp. and takes up much less space in the engine compartment.
The Mazda RX-8 car was specially developed for the new engine, which, according to the brand manager of Mazda Motor Europe Martin Brink, was created according to a new concept - the car was “built” around the engine. As a result, the weight distribution along the axes of the RX-8 is ideal - 50 to 50. The use of a unique shape and small dimensions of the engine made it possible to place the center of gravity very low. "The RX-8 isn't a racing monster, but it's the best handling car I've ever driven," Martin Brink enthused Popular Mechanics.
Barrel of honey...
Without a doubt, at first glance, a rotary piston engine has a lot of advantages over traditional internal combustion engines:
- 30-40% fewer parts;
- Smaller in 2-3 times dimensions and weight, in comparison with the standard internal combustion engine corresponding in power;
- Smooth torque response over the entire rpm range;
- Absence of a crank mechanism, and, consequently, a much lower level of vibration and noise;
- High level of revolutions (up to 15000 rpm!).
A spoon of tar…
It would seem that if the Wankel has such advantages over the piston engine, then who needs these bulky, heavy, rattling and vibrating piston engines? But, as is often the case, in practice, everything is far from so chocolate. Not a single ingenious invention, having left the threshold of the laboratory, was sent to the basket marked "for waste." Serial production was found not on one stone, but on a whole placer of granite:
- Development of the combustion process in a chamber of unfavorable shape;
- Ensuring tightness of seals;
- Ensuring work without warpage of the body in conditions of uneven heating;
- Low thermal efficiency due to the fact that the RPD combustion chamber is much larger than that of a traditional internal combustion engine;
- High fuel consumption;
- High toxicity of gaseous products of combustion;
- A narrow temperature zone for RPD operation: at low temperatures, engine power drops sharply, at high temperatures, rapid wear of the rotor seals.

The only commercially produced rotary motor model to date is the Wankel engine, which belongs to the type of rotary motors with planetary circular motion of the main working element. Such a constructive layout of a rotary engine is undoubtedly the simplest in its own way. technical device, but not the most optimal way of organizing workflows and therefore has its inherent and serious drawbacks.

There are quite a lot of varieties of rotary engines with planetary movement of the main working element, but in essence they differ from each other only in the number of rotor faces and the corresponding shape of the inner surface of the housing. The given schemes different layouts similar motors are taken from the book "Marine Rotary Engines", edition of 1967, authors E. Akatov, V. Bologov and others and prepared for publication in electronic form by the author of this site.

Let's take a brief look at the very design of this type of engine, along with the history of its appearance and scope. The history of the creation of rotary engines with planetary rotational movement of the main working element begins in 1943, when the inventor Mylar proposed the first such scheme. Then, within a short time, several more patents were filed for engines of a similar design. Including the developer of the German company NSU - V. Frede. But the main weak point This scheme of a rotary engine was a system of seals between the ribs at the junction of adjacent faces of a rotating triangular rotor and the walls of a fixed housing. R. Wankel, as a specialist in seals, was involved in solving this complex engineering problem. Soon, thanks to his energy and engineering thinking, he became the leader of the development team. In 1957, a prototype rotary engine of the DKM type was built in the NSU laboratory, with a triangular rotor and a capsule-shaped working chamber in which the rotor was stationary and the housing rotated around it. Much more practical was the KKM-type layout with a normal layout - the working chamber in the housing was stationary, and the rotor rotated in it. This motor appeared a year later, in 1958. In November 1959, NSU officially announced the creation of a working rotary engine. In a short time, about 100 companies around the world have acquired licenses for this technology, with 34 of them being Japanese.

The motor turned out to be very small, powerful and had few parts. In Europe, sales of cars with rotary engines began, but as it turned out, they had a small motor resource, they consumed a lot of fuel and had a very toxic exhaust. The oil crisis of 1973 due to another Arab-Israeli war, when gasoline prices increased several times, sharply raised the question of economy automobile motors. Because of this, in Europe and America, attempts to bring the Wankel rotary engine to the desired degree of perfection were discontinued. But only Japanese company Mazda stubbornly continued to work in this direction. And also soviet plant VAZ - since gasoline at that time in the USSR cost a penny, and a powerful, albeit with a small resource, engine was needed by law enforcement agencies. But in 2004, small-scale production at VAZ was closed and today Mazda is the only automaker that mass-produces cars with a rotary engine. Currently, only one car with a Wankel rotary engine is mass-produced in the world - this is the Mazda RX-8 sports coupe. This machine is equipped with a RENESIS engine with two rotor sections with a total volume of 1.3 liters. The engine is available in several versions with power from 200 to 250 hp.

After overview of the history of a rotary engine with a planetary motion of the rotor, let us dwell on the consideration of its advantages and disadvantages. ADVANTAGES of the Wankel rotary engine compared to traditional piston engines: 1) Increased specific power (hp / kg), it is almost twice that of piston 4 stroke engines. The mass of unevenly moving parts in the Wankel engine is much less than in piston engines of similar power, and the amplitude of such unbalanced movements is noticeably smaller. This is due to the fact that in the "piston" reciprocating movements are carried out, and in the Wankel engine - rotational, planetary circuits. In addition, the Wankel engine lacks a crankshaft and connecting rods.

The fact that such a single-rotor design engine produces power for three-quarters of each revolution of the output shaft also plays into the increased power of the Wankel. Unlike a single cylinder 4 stroke piston engine which only delivers power for one quarter of each revolution of the output shaft. It is for these reasons that much big power. With a working chamber volume of 1300 cm 3, the Mazda RX-8 has a power of 200 hp - 250 hp, and the previous Mazda model RX-7, with an engine of the same size, but with a turbocharger, produced 350 hp.

That is why a special feature of the Mazda RX is its excellent dynamic performance:

in low gear, it is possible to accelerate the car above 100 km / h without undue load on the engine at higher engine speeds (8000 rpm or more).
the Wankel engine is much easier to mechanically balance and get rid of vibration, which makes it possible to increase the comfort of light vehicles such as microcars;
the overall dimensions of a rotary piston engine are 1.5-2 times smaller in relation to a piston engine of comparable power.

The Wankel engine has 35-40% fewer parts.

Flaws:

1) The short stroke length of the face of the triangular rotor. Although it is difficult to compare these indicators directly with a piston motor - the types of piston and rotor movements are too different, but the Wankel engine has about a fifth less stroke length. There is one fundamental difference between the Wankel and the piston engine - the “piston” has an increase in volume in the direction of one linear direction, which coincides with the direction of the stroke. But for Wankel, this movement is complex and only part of the trajectory of the triangular rotor with planetary movement becomes the actual line of the working stroke. (FIG.) This is why the Wankel engine has poorer fuel efficiency than piston engines. Therefore, due to the short stroke length, the temperature is very high. exhaust gases- the working gases do not have time to transfer their main pressure to the rotor, as the exhaust window already opens and hot high-pressure gases with volumetric fragments of the working mixture that have not yet stopped burning exit into the exhaust pipe. Therefore, the exhaust gas temperature of the Wankel engine is very high.

2) The complex shape of the "crescent" combustion chamber. Such a combustion chamber has a large surface of contact of gases with the walls of the housing and the rotor. Therefore, a significant part of the heat is spent on heating the engine parts, and this reduces the thermal efficiency and increases the heating of the motor. In addition, this form of the combustion chamber leads to a deterioration in mixture formation and a slowdown in the combustion rate of the working mixture. Therefore, the Mazda RX-8 engine has 2 spark plugs on one rotor section. These features also negatively affect the level of thermodynamic efficiency.

3) Potentially low torque for a rotary motor. In order to remove rotation from a moving rotor, the center of rotation of which itself continuously performs planetary rotation along a circular path around the geometric center of the working chamber, this engine uses disks eccentrically located on the main shaft. In fact, these are elements of a crank device. That is, the Wankel engine could not completely get rid of the main drawback of the classic piston internal combustion engines - the crank - connecting rod mechanism. Although it is presented in the Wankel motor in its lightweight version - in the form of an eccentric shaft, but the main flaws of this mechanism: a torn, pulsating torque mode and a small arm of the main element that perceives torque - remained “not cured”. (FIG.) That is why a single-section Wankel is inefficient and you need to make 2 or 3 rotor sections to obtain normal performance, it is also desirable to put an additional flywheel on the shaft. In addition to the presence of a crank mechanism in the Wankel engine, the low torque for a rotary engine is also affected by the fact that the kinematic scheme of such a motor is very irrational in terms of perception of the pressure of the expansion working gases by the rotor surface. Therefore, only a certain part of the pressure - about a third - is translated into the working rotation of the rotor and creates a torque. We'll talk more about torque in a special section of the site.

For details on the principle of torque generation in a Wankel rotary engine, see the TORQUE page of the website.

4) The presence of vibrations in the body. The fact is that the system of a rotary motor with a planetary movement of the working element implies a non-equilibrium movement of this body. Those. during rotation, the center of mass of the rotor performs a continuous rotational movement around the center of mass of the body and the radius of this rotation is equal to the shoulder of the eccentric of the main motor shaft. That is why a constantly rotating force vector equal to centrifugal force arising on the rotor. That is, the rotor, when rotating on an eccentric shaft rotating in turn, has inevitable and pronounced elements of oscillatory motion in the nature of its movement. Which leads to the inevitability of vibrations. (RICE.)

5) Rapid wear mechanical radial seals at the corners of the rotor triangle, since they are subjected to a strong radial load, which is inevitable in the Wankel engine by its very principle of operation. (RICE.)

6) The constant threat of a breakthrough of high-pressure gases from the cavity of one working cycle to the cavity of another cycle. This is because the contact of the radial seal between the rotor fin and the combustion chamber wall occurs in one thin line. At the same time, there is still the problem of gas breakthrough through the plug installation sockets when the rotor rib passes over them.

7) Sophisticated lubrication system of the rotating rotor. In the Mazda RX-8 engine, special nozzles inject oil into the combustion chambers to lubricate the rotor fins rubbing against the walls of the combustion chamber during rotation. This increases the toxicity of the exhaust and at the same time makes the engine very demanding on the quality of the oil. In addition, at high speeds, there are increased requirements for lubrication of the cylindrical surface of the eccentric part of the main shaft, around which the rotor rotates, and which removes the main force from the rotor and translates into shaft rotation. It was these two technical difficulties, which are very difficult to solve, that led to insufficient lubrication at high speeds of the most friction-loaded parts of such an engine, and this, accordingly, sharply reduced the engine's service life. It was the insufficient solution of such technical problems that led to a very small resource of Wankel engines, which were produced by the domestic AvtoVAZ. (FIG. - indicate the cylindrical contact surface of the inner socket of the rotor and the eccentric of the shaft disk)

8) High demands on the accuracy of the execution of parts of complex shape make such a motor difficult to manufacture. Such production requires high-precision and expensive equipment - machines capable of creating complex volumes of a working chamber with a curved epitrochoidal surface. The rotor itself also has the shape of a complex triangle with convex surfaces.

As can be seen from the content of this section of the site, the Wankel rotary engine has pronounced advantages, and a large number of almost insurmountable shortcomings that did not allow this type of engine to displace piston engines from the arsenal modern technology. Although such prospects were seriously discussed in the late 60s and early 70s of the last century, and in analytical reviews opinions were expressed that by the end of the 80s of the 20th century, more than half of the world's cars will already have rotary engines different types…. And, despite the presence of negative features and technical difficulties, the Wankel rotary engine was able to appear technically and take place as a commercially viable type of product, because the shortcomings of its main competitors - piston engines with a crank - connecting rod mechanisms turn out to be even more serious and numerous. And this, despite more than a century of attempts to improve them.

CONTINUED ABOUT WANKEL ROTARY ENGINE

September 2016 One of the most difficult problems of all types of rotary engines is the creation of an efficient sealing system, which must create a closed volume in the working chambers of a rotary engine. So far, this is one of the main difficulties in the Tverskoy-type scheme. There it is necessary to make an effective and difficult to manufacture sealing system. And in order to train my hand and get positive experience in such a matter, I decided to create a small working copy of the Wankel engine right from scratch. The work is already coming to an end - I am attaching a photo of such a motor.

Seals

The approximate power of one such rotor section is expected to be about 35-40 hp. A motor of 2 rotor sections is expected to have a power of 70-80 hp.

WANKEL ENGINE - DECEMBER
December 25, 2016 The production of the small Wankel is proceeding at an optimal pace. The engine is ready for 95%, small details remain.
Since on some sites on the Internet these photos of mine are already being discussed and a lot of fantasies are being wound around them, I inform you.
The engine was created from ZERO, there is not a single part from foreign models in it. It does not contain parts from Sachs Wankel, which have not been produced for 30 years, nor from modern small modern aixro, etc., etc.
The engine housing is made of structural alloyed heat-resistant steel subjected to thermochemical hardening. The hardness of the surface layer is 70 HRC. The depth of the heat-strengthened layer is on average 1.5 mm. The radial and mechanical seals are treated in the same way and brought to the same hardness and wear resistance. The engine is air-cooled, lubricating oil will be supplied to the compression chamber through 2 special nozzles. Those. there will be no need to mix oil with gasoline as in 2-stroke engines.

The engine was put on a lathe and subjected to a cold break-in for several hours. This made it possible to evaluate the operation of the seals and the tightness of the resulting sections in the engine as quite safe. In the near future, the pressure that is obtained in the compression sector of the motor will be measured.
The start of the engine is scheduled for the end of January.

RESUME AFTER A PAUSE

After a break, active work resumed. Now (March-May 18) there are active test scrolling of a small experimental engine model. According to its results, seals are being finalized - the most difficult and delicate element in rotary engines. The results are very encouraging.