A turbocharger is actually an air compressor that compresses air to increase air intake.It USES the inertia impulse of exhaust gas from the engine to drive the turbine in the turbine chamber. The turbine also drives the coaxial impeller, which presses the air sent by the air filter pipe to pressurize the air into the cylinder.When the engine speed increases, the exhaust gas discharge speed and turbine speed also increase synchronously. The impeller compresses more air into the cylinder. With the increase of air pressure and density, more fuel can be burned.
First, the general structure of the turbocharger, exhaust gas turbocharger is mainly composed of pump wheel and turbine, of course, there are some other control elements.The pump wheel and turbine are connected by a shaft, namely the rotor. The exhaust gas from the engine drives the pump wheel. The pump wheel drives the turbine to rotate.Turbocharger installed on the exhaust side of the engine, so the working temperature of the supercharger is very high, and the supercharger rotor speed at work is very high, can achieve the similar RPM, high rotation speed and temperature makes common mechanical needle or ball bearing cannot work for the rotor, so the whole floating bearing widely used turbocharger, the engine oil for lubrication, and cooling liquid cooling for the supercharger.Before, turbochargers are mostly used in diesel engines, because gasoline and diesel combustion mode is not the same, so the engine turbocharger form is also different.
Gasoline engine is different from diesel engine, it is not air into the cylinder, but the mixture of gasoline and air, too much pressure is easy to deflagration.Therefore, the installation of turbochargers must avoid deflagration, which involves two related problems, one is the high temperature control, the other is the ignition time control.
After mandatory supercharging, the temperature and pressure of gasoline engine during compression and combustion will increase, and the deflagration tendency will increase.In addition, the exhaust temperature of gasoline engine is higher than that of diesel engine, and it is not suitable to increase the overlap Angle of valve (the time when the inlet and exhaust doors are opened at the same time) to strengthen the cooling of exhaust, reducing the compression ratio will cause insufficient combustion.In addition, the speed of gasoline engine is higher than that of diesel engine, and the air flow rate changes greatly, which is easy to cause the reaction lag of turbocharger.In view of a series of problems in the use of turbochargers in gasoline engines, engineers have made targeted improvements one by one, so that gasoline engines can also be used in exhaust gas turbochargers.
Temperature increase, so not only affect the efficiency of inflation, but also prone to deflagration.Therefore, the device to reduce the intake temperature is called the intercooler.It is installed between the outlet of the turbocharger and the intake pipe to cool the air entering the cylinder.An intercooler is like a radiator, cooled by wind or water, through which the heat of the air escapes into the atmosphere.According to the test, good performance of the intercooler can not only make the engine compression ratio can maintain a certain value without deflagration, but also reduce the temperature can increase the intake pressure, further improve the effective power of the engine.
Due to the wide range of gasoline engine speed and large change in air flow, the compressed impeller shape of turbocharger is a complex ternary curved surface ultra-thin-walled impeller blade, which generally has 12 ~ 30 blades arranged in a radial curve, and the blade thickness is below 0.5 mm. It is made of aluminum by special casting method.The blade shape directly affects the performance of turbocharged engine.The more reasonable the shape and Angle of the impeller is, the lighter the mass is, the more sensitive the start of the impeller is, and the smaller the natural defect "response lag" of the turbocharger is.
In addition to lowering the temperature to reduce the possibility of deflagration outside, but also knock transducer, and its role is in produce deflagration, feel abnormal vibration sensor information feedback immediately to the engine ECU (electronic control unit) control system, will be slightly delayed ignition timing, do not produce deflagration back to normal when the ignition timing.
Because the speed of gasoline engine of car is higher than that of diesel engine, the air velocity is fast and the variation range is large, so its turbocharger has higher requirements.Electronic injection system has been widely used in modern car engines. With the cooperation of electronic control technology and new materials, the application of turbocharger in gasoline engines will become more and more common.
Exhaust gas turbochargers used in cars all use a single inlet turbine housing, that is to say, only use the exhaust gas pressure energy, do not need to use other auxiliary energy.Since the speed range of car engine is large, the exhaust gas turbocharger must be equipped with a regulating device, so that the engine can obtain a relatively constant pressure increase within a certain speed range.In addition, gasoline engine is ignition ignition ignition, its compression ratio is limited to a certain range, too high will cause deflagration.Therefore, there is also a deflagration detection and control mechanism, at any time to adjust the ignition advance Angle.
The exhaust gas turbocharger of car is generally installed near the exhaust pipe, and the turbine and impeller are installed in the turbine chamber and the turbocharger respectively.
When no supercharging is required, such as at idle or with the precursors of detonation, some of the exhaust is discharged through the bypass valve without entering the turbocharger.When the engine speed reaches 2000 RPM, the solenoid valve will close the bypass valve and direct the exhaust flow to the turbine side to make the turbine turn.In addition, another design is to adjust the Angle of turbine blade and adjust the turbine speed through the change of resistance, so as to change the amount of supercharging.
Cooling the air makes it shrink and densify, pushes more air into the same volume, and prevents deflagration.Therefore, the turbocharger of the car is equipped with an intermediate cooler, which is generally air-cooled and installed in front of the engine radiator, next to it or in a separate position, and cooled by the car's head-on airflow or its own fan.
The key part of turbocharger is bearing.This type of bearing, named after the lubrication form, is called "full floating bearing", with extremely high working speed and harsh working environment.Therefore, it is very important to ensure lubrication.If the oil supply is slow due to low oil pressure, the bearing will be damaged and the turbocharger will fail.This kind of failure will not occur in normal engine start up, but if the engine oil and oil filter replacement after the first start up, will produce slow oil supply phenomenon, so that the bearing lack of oil lubrication.In this case, after starting to idle running about 3 minutes, not directly to the speed of the turbocharger start speed.Similarly, do not stop the engine immediately after high speed and uphill. Keep the engine idling for about 1 minute, so that the turbocharger bearing, which is still idling, will not be short of oil.Therefore, the use of turbocharger car drivers, must follow the instructions of the manufacturers to operate, but also pay great attention to the quality of oil, it is not suitable for the turbocharger car as a general car operation.