Function of engine intake and exhaust valves

It plays a very important role in engine operation. The operation of a fuel engine consists of four working processes: intake, compression, operation, and exhaust. In order for the engine to run continuously, these four working processes require periodic cycles. In both working processes, the intake and exhaust processes rely on the engine's gas distribution mechanism to accurately deliver combustible mixtures (gasoline engines) or fresh air (diesel engines), as well as exhaust gases emitted after combustion, based on the working order of each cylinder. In the other two working processes, the compression and working processes require isolating the cylinder combustion chamber from the external intake and exhaust channels to prevent gas leakage and ensure the normal operation of the engine. The component responsible for the above work is the valve in the valve train. It's like a person's respiratory system, inhaling and exhaling without it.、

With the development of technology, the rotational speed of automobile engines is getting higher and higher. The rotational speed of modern automotive engines can generally reach over 5500 revolutions per minute. The completion of these four work processes only takes 0.005 seconds. The traditional two valves can no longer complete the ventilation work in such a short time, which affects the improvement of engine performance. One way to solve this problem is to expand the space for incoming and outgoing gases. In other words, exchange time for space. Multi valve technology is the main way to solve the problem. Until the 1980s, the promotion of multi valve technology made a qualitative leap in the overall quality of the engine.

A multi valve engine is a three valve type in which each cylinder has more than two valves, namely, two intake valves and one exhaust valve; A four valve type with two intake and two exhaust valves; A five valve type with three intake valves and two exhaust valves. Currently, most multi valve engines in automobiles are of the four valve type. A four cylinder engine has 16 valves, a six cylinder engine has 24 valves, and an eight cylinder engine has 32 valves. For example, the engine of the Japanese Lingzhi LS400 car has 8 cylinders and 32 valves. Increase the number of valves and corresponding valve train devices, resulting in a more complex structure. Generally, two top camshafts control the valves on both sides of the cylinder combustion chamber centerline. The valves are arranged in inclined positions on both sides of the center of the cylinder combustion chamber to expand the diameter of the atmospheric valve head, increase the airflow passage area, improve ventilation performance, and form a compact combustion chamber with a spark plug in the center, which is conducive to rapid combustion of the mixture.

Some people ask, "Since valves are so good, why not see an engine with more than six valves in one cylinder?"? Thermodynamics has a concept called the curtain area, which refers to the weekly lift of the valve multiplied by the lift of the valve, that is, the space for the valve to open. The larger the curtain area, the greater the space for the valve to open, and the greater the air intake. Taking the engine of Audi 100 as an example, its four valve curtain zone values are half larger than the two valve curtain zone values, and the exhaust state is greater than 70%. Of course, everything has a certain range of applications, which does not mean that the more valves there are, the greater the value of the curtain area. According to expert calculations, when the valve of each cylinder increases to 6, the value of the curtain area will decrease, the more complex the valve is, and the greater the cost. Therefore, the current number of valves in multi valve fuel engines in automobiles is 3 to 5, with four valves being more common.

Taking the gasoline engine as an example, compared to the traditional two valve engine, the former can absorb more air to mix fuel for combustion, save fuel, emit exhaust gas faster, reduce pollution, improve engine power, and reduce noise, which is in line with the development direction of optimizing the environment and saving energy. Therefore, the multi valve technology can be quickly promoted.