Mazda has a sports car that uses this technology.
Brief introduction of rotary engine
At present, reciprocating piston engine is widely used in commercial vehicles. There is also a well-known but rarely used engine, that is, the triangle piston rotor engine. Rotary engine is also called Miller cycle engine. It uses the rotary motion of triangular rotor to control compression and discharge, which is very different from the linear motion of traditional piston reciprocating engine. This kind of engine was invented by a German named Figas Wankel. On the basis of summarizing the previous research results, some key technical problems were solved and the first rotary engine was successfully developed. The general engine is a reciprocating engine. When working, the piston does reciprocating linear motion in the cylinder. In order to convert the linear motion of piston into rotary motion, crank-connecting rod mechanism must be used. But the rotary engine is different, it directly converts the combustion expansion force of combustible gas into driving torque. Compared with the reciprocating engine, the rotary engine eliminates useless linear motion, so the rotary engine with the same power is smaller, lighter, and has lower vibration and noise, which has great advantages. The motion characteristic of rotary engine is that when the center of triangular rotor rotates around the center of output shaft, triangular rotor itself rotates around its center. When the triangular rotor rotates, the internal gear ring centered on the triangular rotor meshes with the gear centered on the output shaft, and the gear is fixed on the cylinder body and does not rotate. The ratio of the number of teeth of the internal gear ring to the number of teeth of the gear is 3 to 2. The above motion relationship makes the motion trajectory of the apex of the triangular rotor (that is, the shape of the cylinder wall) look like an "8". The triangular rotor divides the cylinder into three independent spaces, and each of the three spaces completes intake, compression, work and exhaust in turn. The triangular rotor rotates once, and the engine ignites and does work three times. Because of the above motion relationship, the rotation speed of the output shaft is three times that of the rotor, which is completely different from the motion relationship 1: 1 of the piston and crankshaft of the reciprocating engine.
[Edit this paragraph] Development history of rotary engine
Rotary engine (Wankel engine) is also called Miller cycle engine. It uses the rotary motion of triangular rotor to control compression and discharge, which is very different from the linear motion of traditional piston reciprocating engine. This engine was invented by German felix wankel (1902- 1988). On the basis of previous research results, some key technical problems were solved and the first rotary engine was successfully developed.
Wankel 1902 was born in Germany, and 192 1 to 1926 was employed in the sales department of a science and technology publishing house in Heidelberg. 1924, Wankel set up his own company in Heidelberg, where he spent a lot of time developing rotary engines. From 65438 to 0927, a series of technical problems such as air tightness and lubrication were finally overcome. During World War II, Wankel served in the German Air Force.
195 1 year, Figas Wankel signed a contract with NSU company of Germany to jointly develop rotary engines. 1954 On April 3rd, NSU Company successfully developed the first rotary engine, and conducted a series of tests on this engine in June 5438+0958. 1960, Wankel rotary engine was first publicly discussed at a seminar of the German Institution of Engineers. Three years later, NSU exhibited a new model with Wankel rotor engine at Frankfurt Motor Show. 1964, NSU and Citroen set up a joint venture company COMOBIL in Geneva, and the rotary engine was put on the car for the first time and became a formal product. 1967, Toyo Industrial Co., Ltd. of Japan also installed rotary engines on Mazda cars and began mass production. At that time, people in the industry thought that this kind of engine was compact and light in structure and operated quietly and smoothly, which might replace the traditional piston engine.
Mazda, which has always had a soft spot for new technology, bought this technology from Wankel with huge investment. Because this is a high-tech technology, few people know this technology, and no one can repair the engine when it breaks down, and it consumes a lot of oil. Some people in the automobile industry are skeptical about the market prospect of this engine. When the oil crisis broke out in 1970s, countries were too busy to develop rotary engines. Only Mazda still believes in the potential of rotary engines, and independently researches and produces rotary engines, and has paid a considerable price for this. They gradually overcame the defects of rotary engine, successfully transferred from experimental production to commercial production, and entered the American market with RX-7 sports car equipped with rotary engine, which was impressive.
With the enhancement of global environmental awareness and the exhaustion of petroleum resources, the study of hydrogen as an energy source has become a major issue. Mazda insisted on the rotary engine at that time, which was the most suitable and "clean" in structure, because the water vapor emitted after hydrogen combustion would not pollute the environment. Mazda has reformed the rotor engine of RX-7 sports car, so that it can use hydrogen as fuel. This kind of engine is assembled on Mazda HR-X, and the fuel tank of 1 m3 stores 43 cubic meters of compressed hydrogen, traveling at 60 kilometers per hour for 230 kilometers, which has attracted the attention of people from all walks of life. Because the rotary engine is very different from the traditional engine from production and assembly to maintenance, the development cost is high. In addition, reciprocating piston engine's power, weight, emissions and energy consumption have been significantly improved compared with the past, and the rotary engine has not shown obvious advantages. Therefore, major auto companies have no enthusiasm to develop and utilize it, and only Mazda is struggling to support it.
The general engine is a reciprocating engine. When working, the piston does reciprocating linear motion in the cylinder. In order to convert the linear motion of piston into rotary motion, crank-connecting rod mechanism must be used. But the rotary engine is different, it directly converts the combustion expansion force of combustible gas into driving torque. Compared with the reciprocating engine, the rotary engine eliminates useless linear motion, so the rotary engine with the same power is smaller, lighter, and has lower vibration and noise, which has great advantages.
The motion characteristic of rotary engine is that the center of triangular rotor rotates around the center of output shaft, while the triangular rotor itself rotates around its center. When the triangular rotor rotates, the internal gear ring centered on the triangular rotor meshes with the gear centered on the output shaft, and the gear is fixed on the cylinder body and does not rotate. The ratio of the number of teeth of the internal gear ring to the number of teeth of the gear is 3:2. The above motion relationship makes the motion trajectory of the apex of the triangular rotor (that is, the shape of the cylinder wall) look like an "8". The triangular rotor divides the cylinder into three independent spaces, and each of the three spaces completes intake, compression, work and exhaust in turn. The triangular rotor rotates once, and the engine ignites and does work three times. Because of the above motion relationship, the rotation speed of the output shaft is three times that of the rotor, which is completely different from the motion relationship 1: 1 of the piston and crankshaft of the reciprocating engine.
[Edit this paragraph] Working principle of rotary engine
The general engine is a reciprocating engine. When working, the piston does reciprocating linear motion in the cylinder. In order to convert the linear motion of piston into rotary motion, crank-connecting rod mechanism must be used. But the rotary engine is different, it directly converts the combustion expansion force of combustible gas into driving torque. Compared with the reciprocating engine, the rotary engine eliminates useless linear motion, so the rotary engine with the same power is smaller, lighter, and has lower vibration and noise, which has great advantages.
The motion characteristic of rotary engine is that the center of triangular rotor rotates around the center of output shaft, while the triangular rotor itself rotates around its center. When the triangular rotor rotates, the internal gear ring centered on the triangular rotor meshes with the gear centered on the output shaft, and the gear is fixed on the cylinder body and does not rotate. The ratio of the number of teeth of the internal gear ring to the number of teeth of the gear is 3: 2. The above motion relationship makes the motion trajectory of the apex of the triangular rotor (that is, the shape of the cylinder wall) look like an "8". The triangular rotor divides the cylinder into three independent spaces, and each of the three spaces completes intake, compression, work and exhaust in turn. The triangular rotor rotates once, and the engine ignites and does work three times. Because of the above motion relationship, the rotation speed of the output shaft is three times that of the rotor, which is completely different from the motion relationship 1: 1 of the piston and crankshaft of the reciprocating engine.
Comparison between rotary engine and traditional reciprocating engine Both reciprocating engine and rotary engine rely on the expansion pressure generated by the combustion of air-fuel mixture to obtain rotating force. The mechanism difference between the two engines lies in the way of using expansion pressure. In the reciprocating engine, the expansion pressure generated by the piston top surface pushes the piston downward, and the mechanical force is transferred to the connecting rod to drive the crankshaft to rotate.
For a rotary engine, the expansion pressure acts on the rotor side. So as to push one of the three faces of the triangular rotor toward the center of the eccentric shaft (see force PG in the figure). This movement is carried out under the action of two components. One is the centripetal force pointing to the center of the output shaft (see Pb in the figure), and the other is the tangential force (ft) that makes the output shaft rotate.
The inner space (or spinning room) of the shell is always divided into three workshops. During the movement of the rotor, the volumes of these three working chambers are constantly changing, and four processes of air intake, compression, combustion and exhaust are successively completed in the swing cylinder. Each process is carried out in different positions of the swing cylinder, which is obviously different from the reciprocating engine. The four processes of reciprocating engine are all carried out in one cylinder.
The displacement of rotary engine is usually expressed by the unit working room volume and the number of rotors. For example, a twin-rotor engine with model 13B has a displacement of "654cc × 2".
Unit studio volume refers to the difference between the maximum volume and the minimum volume of the studio; Compression ratio is the ratio of maximum volume to minimum volume. The same definition also applies to reciprocating engines.
As shown below, the change of working volume of rotary engine and its comparison with four-stroke reciprocating engine. Although in these two engines, the working chamber volume changes smoothly in a wave shape, there are obvious differences between them. The first is the rotation angle of each process: the reciprocating engine rotates 180 degrees, while the rotary engine rotates 270 degrees, which is 1.5 times that of the reciprocating engine. In other words, in a reciprocating engine, the crankshaft (output shaft) rotates twice (720 degrees) in four working processes; However, in a rotary engine, the eccentric shaft rotates three times (1080 degrees) and the rotor rotates one time. In this way, the rotary engine can obtain a longer processing time and form a smaller torque fluctuation, thus making the operation smooth and smooth.
In addition, even at high speed, the rotation speed of the rotor is quite slow, which makes the intake and exhaust time more relaxed, which provides convenience for the operation of the system with higher dynamic performance.
[Edit this paragraph] Application of rotary engine
Now Mazda's rotary engine has been transmitted to RX-8. What progress has RENESIS made this time? Firstly, the area of the air intake hole is increased by 30%, so that the air intake of the engine can meet the demand of 10000 rpm. However, as we all know, this low speed will become very bad, so Mazda has evolved the original three-intake two-stage design into a three-intake three-stage design to avoid the weakness of low speed as much as possible. For high speed, the rotor was hollowed out for the first time, which greatly reduced the weight of the rotor and made the naturally aspirated RX-8 reach the level of 250 horsepower by pulling the speed. However, the most innovative part of RENESIS engine is the exhaust port. In the past, the exhaust port of rotary engine was made on the air chamber wall, and some unburned oil and gas and some lubricating oil were often scraped into the exhaust pipe here, causing pollution problems.
In RENESIS, the exhaust port is located at the front and rear side walls just like the air inlet, which solves the problem of HC pollution in the past, and by the way, the air inlet and exhaust port do not overlap at all, so there will be no problem that the air inlet leaks into the exhaust pipe. It is also possible to open an exhaust hole in the front and rear side walls respectively, so that the exhaust holes of the engine can be changed into two, so as to improve the exhaust efficiency and achieve the purpose of high speed. (I heard that it is already on the 280ps RX-7. ) This is why the RX-8 can generate 250 horsepower at the displacement of 1.3L, and it is still in the state of natural intake. Mazda's rotor engine achievement is not achieved overnight, but through continuous modification bit by bit, the current RX-8 can be created!
[Edit this paragraph] Advantages and disadvantages
The rotor of a rotary engine does work once every revolution. Compared with the general four-stroke engine that does work once every two revolutions, it has the advantage of high horsepower-volume ratio (smaller engine volume can output more power). In addition, due to the axial running characteristics of the rotary engine, it can achieve higher running speed without accurate crankshaft balance. The whole engine has only two rotating parts. Compared with the general four-stroke engine with more than 20 moving parts such as intake and exhaust valves, the structure is greatly simplified and the possibility of failure is greatly reduced. In addition to the above advantages, the advantages of rotary engine include small size, light weight and low center of gravity.
On the contrary, because the three combustion chambers of the rotary engine are not completely isolated, after the engine is used for a period of time, it is easy to cause air leakage due to the wear of oil seal materials, which greatly increases fuel consumption and pollution. Its unique mechanical structure also makes this engine difficult to maintain.
Although the rotary engine has the characteristics of producing high output with small displacement and high rotation speed, due to the different operating characteristics from the reciprocating engine, all countries in the world take the actual displacement of the rotary engine multiplied by two as the comparison benchmark when formulating taxes related to the engine displacement. For example, the RX-8 sports car with rotary engine owned by Mazda in Japan has an actual exhaust volume of only 1.308 cubic centimeter, but in Japan, the exhaust volume of 26 1.6 cubic centimeter is used as the basis for tax classification calculation.