Two elements of engine work: air and fuel No matter how to design an engine, we should focus on these two elements. If you want to improve the power and torque of the engine, it is nothing more than improving the fuel supply and air intake of the engine. It is easy to increase the oil supply, but difficult to increase the air intake. Because air has specific physical characteristics, the ability of natural inhalation alone is limited. As a result, the exhaust gas turbocharging technology, which was once a great success in diesel engines, was transplanted to gasoline engines.
The exhaust gas from the engine is high temperature and high pressure, and is usually discharged outside the vehicle through three-way catalysis, muffler and exhaust pipe. Exhaust gas turbocharged engines use exhaust gas. Through a turbine located in the exhaust pipe, the pressure of exhaust gas can drive the turbine to rotate at a high speed, and through a linkage device, the turbine can drive another turbine located in the intake position to rotate at a high speed (up to tens of thousands of revolutions per minute). The intake turbine compresses fresh air by rotating, which greatly increases its density. The temperature of high-pressure gas is very high, which is not suitable for engine combustion. It needs to be cooled by intercooler before being used by the engine. Through turbocharging, the power and combustion efficiency of the engine can be greatly improved. Take 1.8T as an example, which can be equivalent to a 2.3 naturally aspirated engine. Small displacement and high power represent the highest level of current engine technology.
Most importantly, the maximum torque of the engine can be kept at a maximum of 2 1 0 from1and 750-4600 rpm, that is, the engine torque curve presents a platform structure, which is the highest goal of automobile engine design. The maximum torque range of the engine is particularly large, which makes the driver feel at any speed and the power is endless. This is the height that any naturally aspirated engine in the world can't reach.
When buying a car, you will often see a T behind many car models, such as Bora/KOOC-0/.8t, Audi A6/KOOC-0/.8t, Volkswagen Passat/KOOC-0/.8t and so on. Dealers will tell you that these models with T are equipped with turbocharged engines, which have better power and fuel economy than ordinary engines. So what role does the turbocharger play in the engine? Why can he effectively improve the power output?
In fact, the letter T is the abbreviation of the word Turbo. His structure is simple, but his function can not be ignored. As we all know, ordinary engines suck air into the cylinder when the piston goes down. Turbocharged engines compress air first and then suck it into cylinders. In this way, the air density in the cylinder is higher, so the number of oxygen molecules per unit volume increases, so better air intake effect can be obtained. The direct benefit of this is that the energy released by combustion increases and the power is improved. Moreover, this power has not been improved a little. Usually, a four-cylinder engine equipped with turbocharging can be equivalent to the output of a six-cylinder engine if the turbocharging value is high enough. So how is air compressed? How is compressed air sucked into the cylinder? (pictured)
The related pictures of this theme are as follows:
The above picture shows the working principle of a simple turbocharging system. The blue one is the intake pipe and the red one is the exhaust pipe. It is easy to see from the direction of the arrow in the figure that the exhaust gas discharged from the engine cylinder is introduced into the exhaust turbine through the exhaust pipe. Because the engine exhaust gas has the characteristics of high temperature and high pressure, it contains a lot of energy. These energies are enough to drive the exhaust gas turbine to rotate at a high speed of 654.38+ million revolutions per minute. The exhaust turbine drives the intake turbine to rotate at the same speed through the intermediate shaft, which can compress a lot of fresh air and improve the air density. Because air will release heat after compression, in order to avoid natural gasoline caused by too high temperature in the cylinder, high-pressure air must be introduced into the intercooler for cooling, which can make the cooled air burn safely in the cylinder.
The related pictures of this theme are as follows:
The above picture shows the structure of turbocharged gas. It is easy to see the working process of turbocharged gas from the arrow in the figure. There is a key mechanism here, which is the lubrication system of the turbine shaft. Don't underestimate this bearing between two turbine blades, its working environment is very bad. It is not difficult to imagine that the exhaust temperature of the engine is very high, and it needs to rotate at a speed of 654.38+ 10,000 revolutions per minute at such a high temperature, which puts high demands on its high temperature resistance and wear resistance. Therefore, the shell of this bearing is specially opened with two holes. Part of lubricating oil is injected through these two holes, so that the intermediate shaft is suspended on the oil film and rotates at high speed, ensuring its better reliability and durability.
Turbochargers are usually divided into different grades according to the diameter of the turbine. The larger the turbine diameter, the stronger the ability to compress air, so the higher the boost value, the greater the power generated by the engine. However, the boost value cannot be increased indefinitely. Because the greater the pressurization value, the more heat will be released after air compression. Due to the limited refrigeration capacity of the central air conditioner, the hot air in the cylinder can easily cause natural gasoline. This will not only fail to achieve the supercharging effect, but also reduce the power of the engine. In severe cases, the cylinder will even explode, causing the whole engine to be paralyzed. Therefore, the turbocharging value is determined by strict calculation and experiment, and cannot be changed at will.
Since the turbocharger can greatly improve the power of the car, why not all cars are equipped with it? There is of course a reason for this. We can think that the turbine is a moving part with a certain mass, so it takes a little time to accelerate from a static state to more than 654.38+ 10,000 revolutions. As we all know, when the engine works at standby speed or low speed, the required air intake is small and the turbine speed is low. However, if the engine accelerates quickly at this time, it suddenly needs a lot of intake air to improve the power output of the engine. At this time, it takes some time for the turbine blades to increase the speed and air intake. Although this time is not long, there will be obvious lag when driving. This phenomenon is called turbo lag. Therefore, the driver will obviously feel a little overwhelmed when starting and accelerating at low speed, but after the engine speed rises, he will feel a surging power suddenly emerge. People often say that turbocharged engines have enough stamina, which is the reason.
In order to solve the hysteresis problem, Audi TT adopts a dual turbocharging solution. The so-called double turbocharging means that two turbochargers are installed on the engine, one is a low-value turbocharging with a smaller diameter, which is used when the engine speed is low; One is a large-diameter high-value supercharger, which is only started when the engine speed is high. This can alleviate the turbine lag phenomenon to some extent, but it can't completely cure the problem. However, if the car is equipped with an automatic transmission, the unpleasant feeling caused by the short-term turbine lag will be absorbed by the hydraulic torque converter of the automatic transmission, and the driver will hardly notice it.
It is precisely because of the general hysteresis problem of turbocharging technology that many manufacturers have not used it. Honda, BMW, Ferrari and other automobile manufacturers that emphasize engine responsiveness have never considered the application of turbocharging technology. However, turbocharging also has an obvious advantage, that is, it can make small-displacement engines play the dynamic performance of large-displacement engines, but only the volume of small-displacement engines. Therefore, Porsche is the representative of introducing turbocharging technology into high-performance sports cars. Because Porsche 9 1 1Turbo adopts the rear engine design, the small engine compartment simply can't accommodate 8-cylinder engines. In order to achieve the power effect of an 8-cylinder engine, a turbocharger is installed on a horizontally opposed 6-cylinder engine, and the output power reaches 420 HP, which is equivalent to the power level of an 8-cylinder engine.
Dealers often say that turbine engines are more fuel efficient than ordinary engines, which is true. But many people think that cars with the same 1.8T engine consume more fuel than cars with 1.8 engine. Why is this? In fact, this fuel economy is relative. The turbine drives the turbine through the exhaust gas of the engine. The movement of the turbine will not lose the power of the engine. On the contrary, the compressed intake is more powerful than the ordinary intake. Therefore, the working efficiency of the engine is improved. That is to say, an engine with the same displacement T has higher working efficiency instead of using less oil. Then, if you want to compare fuel consumption, you can't just compare the displacement, you should compare the car with the same power. It must be the turbine that is more economical.
At present, many Japanese manufacturers like to use turbine technology, and the typical representatives are Fuji series and Mitsubishi EVO. In Europe, the earliest introduction of Turbo into cars was Shenbao of Sweden, and later Vortex began to use supercharging technology. There are also two car manufacturers in Germany who like to use turbocharging. The representative models of Audi and Porsche are RS6 and 9 1 1Turbo. These car factories are the world leaders in manufacturing high-performance turbocharged engines!
Turbocharged pumps were first used in airplanes, and then gradually evolved into automobiles.
The main working effect is to increase the power output of the engine and make the engine stronger when the original accessories are inconvenient! However, the use of turbocharging pump also has its own shortcomings, because its main output power is the transmission of power from the exhaust gas emitted by the engine, so it is determined that its working environment is harsh and its working temperature is high, and heat dissipation is very important for it. Both models of Volkswagen series are oil cooled. This is why when many pumps need to be replaced in the later stage, the exhaust gas will smell more or less of engine oil! Because the oil seal in the turbocharger pump has been damaged, it is impossible to seal the oil, and the unsealed oil also flows into the vent of the pump and is discharged together with the exhaust gas.
Many new drivers don't care or even know the precautions of the oil in the turbocharger pump during driving. The following is a brief explanation:
L Cold start requires the driver to move the vehicle after the engine is started and idling for at least 30 seconds in the cold start state of the engine, so as to avoid the fault that the turbine pump rotates too fast due to insufficient lubricating oil pressure after the engine is cold started. The lubrication of turbocharger is realized by the pressure generated after the oil pump works through a special oil pipe. If the vehicle is eager to move after a cold start, the speed and load of the turbocharger pump will increase rapidly, and the oil pressure will be low, so the turbocharger pump will be stuck.
Stop the vehicle after driving at high speed and turn off the engine, because the turbocharger pump is still rotating at high speed under the action of inertia. At this time, the lubrication of the turbine shaft is completed by the work of the oil pump. If the engine stops at this time, all lubrication will stop immediately, and the turbine shaft rotating at high speed will be stuck due to insufficient lubrication, so the correct operation method is to idle for a period of time after running at high speed, about 90 seconds, and then.