What is the turbocharging principle of automobile engine?

Engine turbocharging is the key point of automobile driving. What are the turbocharging principles of automobile engines that I have sorted out below? Welcome to read!

● Function of throttle valve

The engine air intake system has two main components. One is an air filter, which is mainly responsible for filtering impurities in the air; The second is the intake pipe, which mainly introduces air into the cylinder. There is a very important component in the intake pipe, which is the throttle.

The main function of the throttle valve is to control the amount of mixed gas entering the cylinder. So how does it control the air intake? When we drive, the depth of stepping on the accelerator pedal is actually to control the accelerator opening. The deeper the accelerator pedal is pressed, the greater the throttle opening, the greater the intake of mixed gas and the higher the engine speed.

The traditional cable accelerator passes through a steel wire, one end of which is connected with the accelerator pedal and the other end is connected with the accelerator, and its transmission ratio is 1: 1, which leads to unsatisfactory control accuracy. At present, the electronic throttle transmits the data such as the strength and amplitude of stepping on the accelerator pedal to the control unit for analysis through the position sensor, and then summarizes the driver's intention of stepping on the accelerator, and then the ECU calculates the actual throttle opening and gives instructions to control the operation of the accelerator motor, thus realizing accurate control of the accelerator.

● Variable intake manifold length?

We usually see that the length of the intake manifold of the engine seems to be fixed, and its length can be changed? In fact, the control valve is installed in the intake manifold. By opening and closing it, the intake pipe can be divided into two parts, thus changing its effective length. What is the effect of changing the length of the intake manifold? Mainly to improve the intake efficiency of the engine at different speeds, so as to improve the dynamic performance of the engine at various speeds.

When the engine is running at low speed, the black control valve is closed, and the airflow is forced to flow into the cylinder from the long manifold, which can increase the airflow speed and pressure of the intake air, so that gasoline and air can be better mixed and burned more fully (this is a bit like the principle that the water flow speed will increase after the water pipe with slow water flow is crushed). When the engine speed increases, the control valve is opened, and the airflow bypasses the lower pipeline and directly enters the cylinder, so that more air can be sucked in more quickly and the air intake at high engine speed can be increased.

● Why is the exhaust manifold strange?

Automobile exhaust system mainly includes exhaust manifold, three-way catalytic converter, muffler and exhaust pipe. The main function is to discharge the exhaust gas produced by combustion in the cylinder to the atmosphere.

Why do most of the exhaust pipes we see have strange shapes? This design is mainly to avoid the phenomenon that the exhaust gas discharged from each cylinder interferes with each other or the exhaust gas flows back to the maximum extent, which will affect the dynamic performance of the engine.

Although the exhaust pipe design is strange, in order to prevent turbulence, some principles are followed, such as the exhaust manifolds of each cylinder are as independent as possible and the length is as equal as possible; The exhaust manifold is as long as possible, etc.

● How is turbocharging boosted?

Turbocharging is familiar to everyone. You can usually see something like 1 at the back of the car. 4T, 2 .0T, indicating that the engine of this car is turbocharged. Turbocharger is called Turbo or T for short. Turbocharging uses the exhaust gas of the engine to drive the turbine to compress the intake air, thus improving the power and torque of the engine and making the automobile more powerful.

The turbocharger is mainly composed of a turbine and a compressor, which are connected by a transmission shaft. The air inlet of the turbine is connected with the exhaust manifold of the engine, and the exhaust port is connected with the exhaust pipe; The air inlet of the compressor is connected with the air inlet pipe, and the air outlet is connected with the air inlet manifold. How to achieve pressurization? Mainly through the exhaust gas discharged by the engine impacting the turbine to run at high speed, the coaxial compressor is driven to rotate at high speed, and the pressurized air is forced into the cylinder.

Turbocharging mainly uses the energy of engine exhaust gas to drive the compressor to supercharge the intake air. The whole process basically does not consume the power of the engine, and the acceleration continuity is good. But at low speed, the turbine can't intervene in time, which has a certain lag.

● What about mechanical pressurization?

Compared with turbocharging, the principle of supercharger is different. Mechanical supercharging mainly drives a mechanical air compressor to rotate through the power of crankshaft to compress air. Unlike turbocharging, mechanical supercharging will cause a certain degree of loss to the power output of the engine.

Because the supercharger is directly driven by the crankshaft, it will start to work when the engine is running. Therefore, at low speed, the torque output of the engine is also excellent, and the air compression increases linearly according to the engine speed, without the sudden intervention of the turbocharged engine and the low-speed lag of the turbocharged engine. However, when the engine is running at high speed, the power loss of the supercharger is also great, and the power increase is not obvious.

● How does a twin-supercharged engine work?

Double supercharged engine, as its name implies, is an engine equipped with two superchargers. If two turbochargers are used in an engine, it is called a twin-turbocharged engine. Such as BMW 3. The 0L inline six-cylinder engine uses two turbochargers.

Aiming at the turbo lag phenomenon of exhaust gas turbocharging, two identical turbines (one turbocharger for every three cylinders) are connected in parallel on the exhaust pipe. When the engine speed is low, less exhaust gas can drive the turbine to rotate at high speed, generating enough intake pressure and reducing the turbine hysteresis effect.

We have learned before that the turbocharger has hysteresis at low speed, but at high speed, the boost value is large, the engine power is obviously improved, and the engine power is basically not consumed; However, when the engine is running, the supercharger that directly drives the turbine does not have the lag of turbocharging, but only loses some power and the turbocharging value is low. Wouldn't combining them complement each other?

Schematic diagram of dual supercharged engine (turbocharger+supercharger)

Such as 1 equipped on Volkswagen Golf GT. For the 4-liter TSI engine, the designer combined the turbocharger with the supercharger. The supercharger is installed on the intake system of the engine, and the turbocharger is installed on the exhaust system to ensure that the engine can have good supercharging effect at low speed, medium speed and high speed.