A turbocharger is actually an air compressor that increases the intake air volume by compressing air. It uses the inertial impulse of exhaust gas discharged from the engine to push the turbine in the turbine chamber, and the turbine drives the coaxial impeller. The impeller pressurizes the air sent from the air filter pipe to pressurize it into the cylinder. When the engine speed increases, the exhaust gas discharge speed and the turbine speed increase simultaneously, and the impeller compresses more air into the cylinder. The increase in air pressure and density can burn more fuel, increase the amount of fuel and adjust the engine speed accordingly. The output power of the engine can be increased.
Structure principle
Let me first talk about the general structure of the turbocharger. The exhaust gas turbocharger is mainly composed of a pump wheel and a turbine, and of course there are other control components. The pump wheel and the turbine are connected by a shaft, that is, the rotor. The exhaust gas from the engine drives the pump wheel. The pump wheel drives the turbine to rotate. The turbine rotates and then pressurizes the 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 rotor speed is very high when the supercharger is working, which can reach hundreds of thousands of revolutions per minute, such a high speed and temperature As a result, common mechanical needle rollers or ball bearings cannot work for the rotor. Therefore, turbochargers generally use full floating bearings, which are lubricated by oil, and coolant is used to cool the supercharger. In the past, turbochargers were mostly used in diesel engines. Because gasoline and diesel burn in different ways, the form of turbochargers used in engines is also different.
A gasoline engine is different from a diesel engine. It is not air that enters the cylinder, but a mixture of gasoline and air. If the pressure is too high, it is easy to deflagration. Therefore, deflagration must be avoided when installing a turbocharger. Two related issues are involved here, one is high temperature control, and the other is ignition time control.
After forced pressurization, the temperature and pressure during compression and combustion of the gasoline engine will increase, and the deflagration tendency will increase. In addition, the exhaust temperature of gasoline engines is higher than that of diesel engines, and it is not advisable to increase the valve overlap angle (the time when the intake and exhaust valves are opened at the same time) to enhance the cooling of the exhaust. Lowering the compression ratio will cause insufficient combustion. In addition, the speed of the gasoline engine is higher than that of the diesel engine, and the air flow changes greatly, which can easily cause the turbocharger's response to lag. In response to a series of problems arising from the use of turbochargers in gasoline engines, engineers have made targeted improvements one by one so that gasoline engines can also use exhaust gas turbochargers.
Intercooler
The temperature increases, which not only affects the inflation efficiency, but also prone to deflagration. Therefore, it is necessary to install a device to reduce the temperature of the intake air, which is an intercooler. It is installed between the turbocharger outlet and the intake pipe to cool the air entering the cylinder. The intercooler is like a radiator. It is cooled by wind or water, and the heat of the air escapes into the atmosphere through cooling. According to tests, a good-performance intercooler can not only keep the engine compression ratio at a certain value without deflagration, but also reduce the temperature to increase the intake pressure and further increase the effective power of the engine.
impeller
Due to the wide speed range of gasoline engines and the large changes in air flow, the shape of the turbocharger's compression impeller is a complex ternary curved ultra-thin-walled impeller blade. Generally there are 12 to 30 blades arranged in a radial curve. Less than 0.5 mm, made of aluminum with special casting method. The shape of the blades directly affects the performance of the turbocharged engine. The more reasonable the shape and angle of the impeller, the lighter the weight, the more sensitive the impeller's start-up, and the smaller the inherent defect of the turbocharger.
Deflagration sensor
In addition to lowering the temperature to reduce the possibility of deflagration, a deflagration sensor is also used. Its function is that when a deflagration occurs, the sensor feels abnormal vibration and immediately feeds the information to the engine ECU (Electronic Control Unit) control system to switch the ignition The timing is slightly delayed, and the normal ignition timing is resumed when no deflagration occurs.