Working Principle of Turbocharger

The biggest advantage of the turbocharger is that it can greatly increase the power and torque of the engine without increasing the engine displacement. Generally, the power and torque of the engine after adding the supercharger are increased by 20%. ~30%. The disadvantage of the turbocharger is the hysteresis, that is, the inertia of the impeller reacts slowly to the sudden change of the throttle, which causes the engine delay to increase or decrease the output power. This is a bit of an instant for a car that suddenly accelerates or overtakes. a feeling of.

First, let's talk about the general structure of the turbocharger. The exhaust turbocharger is mainly composed of the pump wheel and the 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, and the turbine rotates to pressurize the intake system. The supercharger is installed on the exhaust side of the engine, so the operating temperature of the supercharger is very high, and the speed of the rotor is very high when the supercharger is working, which can reach hundreds of thousands of revolutions per minute, such high speed and temperature. This makes the common mechanical needle roller or ball bearing unable to work for the rotor. Therefore, the turbocharger generally uses a fully floating bearing, which is lubricated by oil, and the coolant is cooled by the supercharger. In the past, turbochargers were mostly used on diesel engines, and some gasoline engines now use turbochargers. Because gasoline and diesel are burned differently, the engine is also different in the form of a turbocharger.

Unlike a diesel engine, a gasoline engine enters a cylinder instead of air, but a mixture of gasoline and air. If the pressure is too high, it is easy to deflagrate. Therefore, the installation of a turbocharger must avoid knocking. There are two related issues involved, one is high temperature control and the other is ignition time control.

After forced pressurization, the temperature and pressure of the gasoline engine during compression and combustion will increase, and the tendency to deflagration will increase. In addition, the exhaust temperature of the gasoline engine is higher than that of the diesel engine, and it is not appropriate to increase the valve overlap angle (the time when the intake and exhaust valves are simultaneously opened) to enhance the cooling of the exhaust gas, and the reduction of the compression ratio may cause insufficient combustion. Also, the speed of the gasoline engine is higher than that of the diesel engine, and the air flow varies greatly, which easily causes the turbocharger reaction to lag. In response to a series of problems with the use of turbochargers in gasoline engines, engineers have made targeted improvements to make the gasoline engine also use the exhaust turbocharger.

Since the car gasoline engine has a higher rotational speed than the diesel engine, the air flow rate is fast and the range of variation is large, its turbocharger has higher requirements. The electronic injection system has been widely used in modern car engines. With the combination of electronic control technology and new materials, the application of turbochargers on gasoline engines will become more and more popular.

The key component of a turbocharger is a bearing. This type of bearing, named after the lubrication form, is called a “full floating bearing” and has a very high operating speed and a harsh working environment. Therefore, ensuring lubrication is very important. If the oil supply is slow due to low oil pressure, the bearing will be damaged and the turbocharger will fail. This type of failure does not occur during normal engine start-up, but if the engine is first started after changing the oil and oil filter, there will be a slow supply of oil, which will make the bearing lack oil lubrication. In this case, it is necessary to idle for about 3 minutes after starting, and it is not possible to directly increase the speed to the turbocharger starting speed. Similarly, do not stop the engine immediately after high speed and uphill, and keep the engine running at idle for about 1 minute, so that the turbocharger bearings that continue to idle will not be short of oil. Therefore, the driver of the turbocharger car must follow the instructions of the manufacturer, but also pay attention to the quality of the oil. It is not appropriate to operate the turbocharger car as a normal car.