The engine generates electricity by burning the fuel in the cylinder. The input amount of fuel is limited by the amount of air sucked into the cylinder, and the generated power is also limited. If the running performance of the engine is in the best state, increasing the output power can only improve the combustion function by compressing more air into the cylinder, thus increasing the fuel quantity. Under the current technical conditions, turbocharger is the only mechanical device that can increase the output power of the engine without changing the working efficiency.

structure

Turbocharger is a machine composed of turbine chamber and supercharger. The inlet of the turbine chamber is connected with the exhaust manifold, and the outlet is connected with the exhaust pipe. The air inlet of the supercharger is connected with the air cleaner pipeline, and the air outlet is connected with the air inlet manifold. The turbine and impeller are installed in the turbine chamber and supercharger respectively, and they are coaxially and rigidly connected.

principle

Turbocharger is actually an air compressor, which increases the air intake by compressing air. It uses the inertia impulse of the exhaust gas discharged by the engine to push the turbine in the turbine chamber, and the turbine drives the coaxial impeller, which pressurizes the air sent by the air cleaner pipeline and sends it to the cylinder. When the engine speed increases, the exhaust gas discharge speed increases synchronously with the turbine speed, and the impeller compresses more air into the cylinder. With the increase of air pressure and density, more fuel can be burned. The output power of the engine can be increased by increasing the fuel quantity and adjusting the engine speed accordingly.

technology

The turbocharger is installed on the intake and exhaust manifold of the engine, and it is under the working conditions of high temperature, high pressure and high speed. Its working environment is very harsh, and its work requirements are harsh, and it requires high materials and processing technology. Among them, the most difficult to manufacture is the "floating bearing" that supports the turbine shaft. Its working speed can reach more than 654.38+100000 rpm, and the ambient temperature can reach more than 600 degrees or 700 degrees, which is by no means affordable for ordinary bearings. Because there is oil between the bearing and the inner wall of the machine body for cooling, it is also called "full floating bearing".

disadvantaged

In addition, although the turbocharger has the function of assisting the engine to boost power, it also has its shortcomings, the most obvious one is "lag response", that is, due to the inertia of the impeller, it responds slowly to the sudden change of the throttle. Even after improvement, the response time will be 1.7 seconds, which will delay the increase or decrease of the engine output power. For a car that wants to suddenly accelerate or overtake, it will feel a little sluggish in an instant.

improve

But after all, turbochargers are unprofitable. It works by using the exhaust gas of the engine, and if it is not used, the energy of these exhaust gases will be wasted. Therefore, since the advent of turbocharger, people often carry out technical transformation on it, such as improving machining accuracy and minimizing the gap between turbine and the inner wall of turbine cavity to improve the energy utilization rate of exhaust gas; The turbocharger can be made more compact and smaller by using new material ceramics, and the "lag response" time of the turbine can be reduced by taking advantage of the advantages of ceramics such as high heat resistance, strong rigidity and light weight.

In recent 30 years, turbochargers have been widely used in many types of automobiles, which make up for the inherent shortcomings of some naturally aspirated engines, and can increase the engine output power by more than 10% without changing the cylinder working volume. Therefore, many automobile manufacturing companies use this supercharging technology to improve the output power of the engine, thus achieving high performance of the automobile.

Graphic turbocharger

Turbocharger is actually an air compressor, which increases the air intake by compressing air. It uses the inertia impulse of the exhaust gas discharged by the engine to push the turbine in the turbine chamber, and the turbine drives the coaxial impeller, which pressurizes the air sent by the air cleaner pipeline and sends it to the cylinder. When the engine speed increases, the exhaust gas discharge speed increases synchronously with the turbine speed, and the impeller compresses more air into the cylinder. With the increase of air pressure and density, more fuel can be burned, and the output power of the engine can be increased by increasing the fuel quantity and adjusting the engine speed accordingly.

Generally, internal combustion engines operate in a "natural intake" mode. This mode uses the vacuum generated inside the cylinder when the piston descends and injects the mixed air pressure into the cylinder with the help of the external atmospheric pressure. However, due to various factors, it is difficult to reach 100%. According to the measured data, the volume ratio of general gasoline engines is about 60%-70%. Even a well-designed engine can only reach about 80%. Because the volume ratio of 1% increases every time, the output power of the engine can increase by about 3%, so people invented the supercharger.

Superchargers were originally used in diesel engines, divided into piston type and centrifugal type, driven by the power output from the engine. Because the diesel engine is ignited by fuel injection, and the compressed air is pure air, unlike the gasoline engine, which is ignited by the high-pressure spark of the spark plug in the process of mixture compression, in order to improve the power, the compression ratio of the diesel engine is already very high, and the power can be increased by 30%~ 100% after adding the supercharger. However, it consumes a part of the output power of the engine, which is not worth the loss for the light gasoline engines used in automobiles and motorcycles, so designers have thought of a method of using exhaust gas to drive the supercharger, that is, the exhaust turbocharger.

The turbocharger consists of a turbine impeller and a compressor impeller mounted on the same turbocharger shaft. The turbocharger shaft is supported by bearings in the turbocharger housing. There are many blades on turbine impeller and compressor impeller. The exhaust gas discharged from the cylinder directly enters the turbine to drive the impeller and supercharger shaft to rotate. Because the compressor impeller is fixed at the other end of the supercharger shaft, the compressor impeller also rotates with the shaft.

The impeller of the compressor is installed in the air inlet pipe. When the impeller rotates, air is sucked into the intake pipe, compressed by the compressor and sent into the intake pipe. Most supercharged engines are port fuel injection engines, and the fuel injected into the port is mixed with compressed air to form a dense air-fuel mixture. As the amount of mixed gas entering the cylinder increases, the engine power increases.

The rotating speed of turbo-charged impeller exceeds 100 000r/min, so the balance of impeller and bearing lubrication are very important. Before the supercharger starts to pressurize the air in the intake pipe, the supercharger shaft must reach a certain speed. Some turbochargers start to compress air when the engine speed is 1 250 rpm, and reach the maximum boost pressure at 2 250 rpm.

First, the control of boost pressure.

If the boost pressure of turbocharger is not limited, too high intake pipe pressure and too high combustion pressure may damage engine parts, so many turbochargers are equipped with deflation bellows. The bleeder valve from the diaphragm box to the turbine shell is connected by a connecting rod, the diaphragm spring presses the bleeder valve to close it, and the pressurization pressure in the intake pipe acts on the diaphragm of the bleeder valve. When the pressurization pressure in the intake pipe reaches the maximum safety limit, the pressurization pressure pushes the deflation diaphragm and opens the air valve, so that part of the exhaust gas does not pass through the turbine wheel, thus limiting the rotational speed and pressurization pressure of the turbocharger shaft. On some engines, the supercharging pressure acting on the deflation diaphragm is controlled by computer, and the supercharging pressure is controlled by PCM opening or closing the electromagnetic coil. Some computers, according to pre-programmed programs, allow a short period of time to generate higher boost pressure during sudden acceleration, so as to improve the acceleration of the engine.

Second, the cooling of the turbocharger.

Exhaust gas flows through the turbine wheel to raise the temperature of the turbocharger, especially when the engine is working under heavy load. Many turbochargers have cooling water pipes from the turbocharger housing to the cooling system, and coolant circulates in the turbocharger housing to cool the shaft and bearings. The oil of the engine lubrication system is supplied from the main oil passage to the bearing and shaft of the supercharger to lubricate and cool the bearing, and then returns to the crankcase through the supercharger housing. The oil seal is installed on the shaft of the supercharger to prevent oil from leaking into the compressor or turbine wheel chamber. If the oil seal is damaged, the oil will escape into the compressor or compressor impeller chamber, resulting in blue smoke in the exhaust and increased fuel consumption.

Some turbochargers are not connected with the cooling water pipe of the turbocharger housing, but are cooled by oil and air. If the engine stops immediately after working at high load or high speed, the engine oil may burn in the bearing of the supercharger cooled by engine oil and air, and the hard carbon particles produced by the combustion will scratch the bearing of the supercharger. If there is coolant circulating in the supercharger housing, the bearing temperature can be lowered to avoid such problems. Therefore, after heavy load or high speed operation, the turbocharger cooled by engine oil and air should be idling at least 1min before shutdown, which is helpful to prevent the turbocharger bearing from being damaged.

Third, the development and application of turbocharging technology abroad

Although the turbocharger has been used in heavy-duty occasions for many years, it was not widely used in automobiles before 1980. Until the appearance of various heat-resistant materials, the problems such as slow acceleration of the turbocharger at low speed and difficult cooling of bearings were gradually solved. Chevrolet first used turbochargers in CORVAIA cars, and later used them in many racing cars. Some use 2~3 turbochargers in series, increasing to 3 atmospheres, reaching several times the power of non-supercharged engines. Honda took the lead in using turbocharger and EFI system to control the fuel supply of CX500 motorcycle engine, making its maximum power reach 57.33kW(8000r/min), while the power of the engine without turbocharger in the same class was only 35.28kW, which increased by 62.5%. Subsequently, Japan's Suzuki Company and Yamaha Company used turbochargers on large-displacement motorcycle engines, and the maximum power and speed of their engines were greatly improved. Since the advent of ceramic materials, it has been used to make "ceramic engine" and "ceramic supercharger" because of its advantages of high hardness, corrosion resistance, heat resistance, thermal shock resistance, high temperature change resistance, self-lubrication and stable performance in high temperature working environment. Without cooling system and lubrication system, the volume can be reduced by 40%, the mass can be reduced by 20% and the service life can be reduced by 65,438+000%.

Four. Technical status and prospect of development and application of turbocharger in China

At present, metal turbochargers have been widely used in automobiles and foreign motorcycles, and ceramic turbochargers and ceramic engines represent the important development direction of this technology. Large domestic automobile and diesel engine manufacturing companies, such as FAW, Erqi, Guangxi Heavy Duty Truck and Yangzhou Diesel Engine, have successfully developed turbochargers, while domestic research on ceramic materials started late, but domestic automotive engines made of ceramic materials have come out. In order to speed up the application of turbocharging technology in domestic motorcycle engines, we should first popularize the application of metal turbocharging technology in large-displacement motorcycles, and at the same time actively carry out the development and application research of ceramic engines and ceramic turbochargers nationwide, so as to promote the application of turbocharging technology in domestic motorcycles as soon as possible.

With the gradual popularization of cars into people's lives, our requirements for cars have also been unconsciously improved. I don't know when it started, but more and more cars with "T" appeared on the road. Why do these cars add a T after the displacement, such as Bora's 1.8T? Haha, let the author tell you that this T stands for turbocharging, which means that you can use the fuel consumption of 1.8L engine to get the power close to that of 2.4L engine! Is there really such a free lunch? The answer is yes. Let's take a look at the "Full Contact of Turbocharged Cars: Basic Literacy" that we have carefully prepared for you!

Classic Bora 1.8T turbocharged engine.

1. What is turbocharging?

First, let's figure out what turbocharging is. The English name of turbocharging is Turbo. Generally speaking, if we see Turbo or T at the rear of a car, it means that the engine used in this car is a turbocharged engine. I believe you have seen many such models on the road, such as Audi A6 1.8T, Passat 1.8T, Bora 1.8T and so on.

Turbocharging kit

The main function of turbocharging is to increase the air intake of the engine, thus improving the power and torque of the engine and making the car more dynamic. After the engine is equipped with turbocharger, its maximum power can be increased by 40% or even higher than that without turbocharger. This means that the same engine can generate more power after being supercharged. Take our most common 1.8T turbocharged engine as an example. After supercharging, the power can reach the level of 2.4L engine, but the fuel consumption is not much higher than that of 1.8 engine. Another level is to improve fuel economy and reduce exhaust emissions.

However, the pressure and temperature of the supercharged engine are greatly increased, so the life of the engine will be shorter than that of the engine with the same displacement, and the mechanical performance and lubrication performance will be affected, which also limits the application of turbocharging technology in the engine to some extent.

Second, the principle of turbocharging

The earliest turbochargers were used in sports cars or formula racing cars, which made the engine gain more power in those racing competitions with limited engine displacement.

Red is high-temperature waste gas, and blue is fresh air.

As we all know, the engine generates electricity by burning the fuel in the cylinder. Because the fuel input is limited by the amount of air sucked into the cylinder, the power generated by the engine is also limited. If the running performance of the engine is in the best state, increasing the output power can only increase the fuel quantity by compressing more air into the cylinder, thus improving the combustion function. Therefore, under the current technical conditions, the turbocharger is the only mechanical device that can increase the output power of the engine without changing the working efficiency.

The turbocharging device we usually talk about is actually an air compressor, which increases the air intake of the engine by compressing air. Generally speaking, turbocharging is to use the inertia impulse of the exhaust gas discharged by the engine to drive the turbine in the turbine room, and the turbine drives the coaxial impeller to pressurize the air sent by the air cleaner pipeline into the cylinder. When the engine speed increases, the exhaust gas discharge speed increases synchronously with the turbine speed, and the impeller compresses more air into the cylinder. With the increase of air pressure and density, more fuel can be burned. The output power of the engine can be increased by increasing the fuel quantity and adjusting the engine speed accordingly.

You may think that the turbocharger is complicated, but it is not. Turbocharging device is mainly composed of turbine chamber and supercharger. First, the air inlet of the turbine chamber is connected with the exhaust manifold of the engine, and the air outlet is connected with the exhaust pipe. Then the air inlet of the supercharger is connected with the air cleaner pipeline, and the air outlet is connected with the air inlet manifold. Finally, the turbine and the impeller are respectively installed in the turbine chamber and the supercharger, and are coaxially and rigidly connected. Such an integrated turbocharging device is completed, and your engine is "overclocked" like a computer CPU.

Third, the types of turbocharging.

1. Mechanical supercharging system: This device is installed on the engine and connected with the crankshaft of the engine through a belt. It gets power from the output shaft of the engine and drives the rotor of the supercharger to rotate, thus blowing the supercharged air into the intake manifold. Its advantage is that the turbine speed is the same as the engine speed, so there is no lag phenomenon and the power output is very smooth. But because it is installed in the rotating shaft of the engine, it still consumes some power, and the effect of supercharging is not high.

2. Air wave pressurization system: air is compressed by pulse air wave of high-pressure waste gas. This system has good supercharging performance and acceleration performance, but the whole device is huge and not suitable for installation in small cars.

3. Exhaust gas turbocharging system: This is the most common turbocharging device in our daily life. The turbocharger has no mechanical connection with the engine, but is actually an air compressor, which increases the intake air by compressing air. It uses the inertia impulse of the exhaust gas discharged by the engine to push the turbine in the turbine chamber, and the turbine drives the coaxial impeller, which pressurizes the air sent by the air cleaner pipeline and sends it to the cylinder. When the engine speed increases, the exhaust speed and the wheel speed also increase synchronously, and the impeller compresses more air into the cylinder. With the increase of air pressure and density, more fuel can be burned, and accordingly, the output power of the engine can be increased by increasing the fuel quantity. Generally speaking, after installing the exhaust gas turbocharger, the engine power and torque will be increased by 20%-30%. However, exhaust gas turbocharging technology also has its own points that must be paid attention to, that is, the pump wheel and turbine are connected by a shaft, that is, the rotor. The exhaust gas from the engine drives the pump wheel, which drives the turbine to rotate, and the turbine rotates to pressurize the air intake system. The supercharger is installed on the exhaust side of the engine, so the working temperature of the supercharger is very high, and the rotating speed of the supercharger rotor is very high, which can reach hundreds of thousands of revolutions per minute. Such a high speed and temperature make the ordinary mechanical needle roller or ball bearing unable to work for the rotor, so the turbocharger generally adopts full floating bearing, which is lubricated by oil and cooled by coolant.

4. Compound supercharging system: that is, exhaust gas turbocharging and mechanical supercharging are used together. This device is widely used in high-power diesel engines, with high engine output power, low fuel consumption rate and low noise, but its structure is too complicated, its technical content is high, and it is difficult to maintain and popularize.

Fourth, the shortcomings of turbocharged engines

It is true that turbocharging can improve the engine power, but it also has many shortcomings, the most obvious of which is the lag of power output response. Let's take a look at the working principle of turbocharging, that is, due to the inertia of the impeller, the reaction to the sudden change of the throttle is slow, that is to say, there is a time difference between your big foot stepping on the throttle and the rotation of the impeller, and more air is pushed into the engine to gain greater power, which is not short. Generally speaking, improved turbocharging also takes at least 2 seconds to increase or decrease the power output of the engine. If you want to accelerate suddenly, you will feel that you can't accelerate instantly.

With the development of technology, although various manufacturers who use turbochargers are improving the technology of turbochargers, because of the design principle, driving a turbocharger car is still a little surprising compared with driving a large-displacement car. For example, if we buy a 1.8T turbocharged car, the acceleration in actual driving is definitely not as good as 2.4L, but as long as we wait for the waiting period, the power of 1.8T will come up, so if you pursue the feeling of driving, the turbocharged engine is not suitable for you. Turbocharging will be especially useful if you are running at high speed or something.

If your car often drives in the city, you really need to consider whether it needs turbocharging, because the turbine is not always started. In fact, in daily driving, turbocharging is rarely started or even used, which has an impact on the daily performance of turbocharged engines. Take the turbocharging of Subaru (Fuji) impreza as an example. Its starting time is about 3500 rpm, and the most obvious power output point is about 4000 rpm. At this time, there will be a feeling of secondary acceleration, which lasts until 6000 rpm or even higher. Generally speaking, when we are driving in urban areas, the shift is only between 2000 and 3000, and the estimated speed of the fifth gear is 120, which means that unless you deliberately stay in the low gear, the turbocharging with the speed not exceeding 120 km/h cannot be started at all. Without the start of turbocharging, your 1.8T is actually just a car with 1.8 power, and the power of 2.4 can only be your psychological function.

In addition, turbocharging has maintenance problems. Take Bora's 1.8T as an example, the turbine will be replaced about 60,000 kilometers. Although the frequency is not too much, after all, it invisibly adds a maintenance fee to your car, which is particularly noteworthy for car owners whose economic environment is not particularly good.

Verb (abbreviation for verb) The use of turbocharged engines

The turbocharger uses the exhaust gas from the engine to drive the turbine. No matter how advanced, it is still a set of mechanical devices. Because it often works at high speed and high temperature, the exhaust gas turbine end temperature of the turbocharger is above 600 degrees, and the rotating speed of the turbocharger is also very high. Therefore, in order to ensure the normal operation of the turbocharger, it is very important to use and maintain it correctly. Mainly should follow the following methods:

1. Don't slam on the accelerator after the car engine starts. You should rest for three minutes first. This is to increase the temperature of the engine oil, improve the fluidity and make the turbocharger fully lubricated. Then you can increase the engine speed and start driving. This is especially important in winter, and it takes at least five minutes to warm up the car.

2. After the engine runs at high speed for a long time, it cannot be turned off immediately. The reason is that when the engine is working, part of the engine oil is supplied to the turbocharger rotor bearing for lubrication and cooling. After the running engine stops suddenly, the oil pressure drops to zero rapidly, the oil lubrication will be interrupted, and the heat inside the turbocharger cannot be taken away by the oil. At this time, the high temperature of the turbine part of the turbocharger will be transferred to the middle, and the heat in the bearing support shell cannot be taken away quickly, while the turbocharger rotor is still rotating at high speed under the action of inertia. This will lead to "jamming" between the rotating shaft and the shaft sleeve of the turbocharger, and damage the bearing and shaft. In addition, after the engine is suddenly turned off, the temperature of the exhaust manifold is very high at this time, and its heat will be absorbed into the turbocharger housing, and the engine oil stranded in the turbocharger will be boiled into carbon deposit. When this carbon deposit accumulates more and more, it will block the oil inlet, lead to the lack of oil in the shaft sleeve and accelerate the wear between the turbine shaft and the shaft sleeve. Therefore, the engine should be idling for three minutes before flameout to reduce the rotor speed of turbocharger. In addition, it is worth noting that turbocharged engines are not suitable for long-term idle running, and should generally be kept within 10 minutes.

3. Pay attention to the choice of engine oil. Due to the function of turbocharger, the quality and volume of air entering the combustion chamber are greatly improved, and the engine structure is more compact and reasonable. The higher compression ratio makes the engine work harder. The machining accuracy is also higher, and the assembly technical requirements are stricter. All these determine the high temperature, high speed, high power, high torque and low emission characteristics of turbocharged engine. At the same time, it also determines that the internal parts of the engine should bear higher temperature and greater impact, extrusion and shear force. Therefore, when selecting engine oil for turbocharged vehicles, its particularity should be considered. The engine oil used must have good wear resistance and high temperature resistance, and a lubricating oil film block with high oil film strength and stability should be established. Synthetic engine oil or semi-synthetic engine oil can just meet this requirement, so in addition to the engine oil specified by the original factory, it is best to use high-quality lubricating oil such as synthetic engine oil and semi-synthetic engine oil.

4. The oil and filter must be kept clean to prevent impurities from entering, because the fit clearance between the rotating shaft and the shaft sleeve of the turbocharger is very small. If the lubricating ability of the oil decreases, the turbocharger will be scrapped prematurely.

5, need to clean the air filter on time, to prevent impurities such as dust from entering the high-speed rotating compressor impeller, leading to unstable speed or aggravating the wear of the shaft sleeve and seal.

6. Regularly check whether the sealing ring of turbocharger is a bee. Because if the sealing ring is not sealed, the exhaust gas will enter the engine lubrication system through the sealing ring, making the oil dirty and the crankcase pressure rising rapidly. In addition, when the engine is running at low speed, the engine oil will also be discharged from the exhaust pipe through the sealing ring or enter the combustion chamber for combustion, resulting in excessive consumption of engine oil and "burning engine oil".

7. The turbocharger should always check whether there is abnormal sound or vibration, and whether the lubricating oil pipes and joints are leaking.

8. The precision of turbocharger rotor bearing is very high, and the working environment of maintenance and installation is very harsh. Therefore, when the turbocharger fails or is damaged, it should be repaired at the designated maintenance station instead of the ordinary repair shop.