On January 29, 1886, Karl Benz, a German, installed his four-stroke single-cylinder fuel engine on a three-wheeled car and obtained the patent, and the world began to have a real automobile from this day. The engine created the car, so to speak. The basic structure of the engine (as shown in the figure) is composed of cylinder 1, piston 2, connecting rod 3, crankshaft 4 and other main parts. Each cylinder has at least two valves, one intake valve (blue) and one exhaust valve (orange).

Valve device is a component of engine valve mechanism, which plays a very important role in engine operation. The operation of fuel engine consists of four working processes: intake, compression, work and exhaust. To make the engine run continuously, it is necessary to make the four working processes cycle, sequence and timing cycle work. Two of these processes, the intake and exhaust processes, rely on the engine's valve mechanism to accurately transport the combustible mixture in accordance with the working sequence of each cylinder, as well as the exhaust gas after combustion. The other two working processes, compression and work process, must be isolated from the cylinder combustion chamber and the external inlet and exhaust channel, do not let the gas leakage to ensure the normal operation of the engine. The part responsible for the above work is the valve in the valve mechanism. It is like a person's breathing organ, inhalation and exhalation, lack of it.

With the development of technology, the speed of automobile engine has become higher and higher. The speed of modern car engine can generally reach more than 5500 revolutions per minute, and it only takes 0.005 seconds to complete the four working processes. The traditional two valves are no longer competent to complete the air exchange work in such a short time, limiting the improvement of engine performance. The only way to solve this problem is to expand the space in which the gas enters and exits. In other words, trading space for time. Multi-valve technology is the best way to solve the problem. It was not until the popularization of multi-valve technology in the 1980s that the overall quality of the engine had a qualitative leap. Multi-valve engine refers to the valve number of each cylinder more than two, that is, two intake valves and a three-valve type exhaust valve; Four-valve type with two intake valves and two exhaust valves; Five-valve type with three intake valves and two exhaust valves.

At present, the multi - valve engine on the car is four - valve type. Four-cylinder engines have 16 valves, six-cylinder engines have 24 valves, and eight-cylinder engines have 32 valves. For example, the Japanese Lexus LS400 sedan engine is 8 cylinders 32 valves. To increase the number of valves, it is necessary to increase the corresponding valve mechanism device. The structure is more complex. Generally, two overhead camshafts are used to control the valves arranged on both sides of the center line of the cylinder combustion chamber. The valve is arranged on the inclined position on both sides of the center of the cylinder combustion chamber, in order to maximize the diameter of the valve head, increase the air flow through the area, improve air exchange performance, and form a compact combustion chamber with the spark plug in the center, which is conducive to the rapid combustion of the mixture.

Some people ask, since the valve is so good, why not see a cylinder of more than 6 valve engine? Thermodynamics has a concept called the curtain zone, which refers to the circumference of the valve multiplied by the lift of the valve, or the space in which the valve is open. The larger the curtain area, the greater the opening space of the valve and the greater the intake volume. In the case of the Audi 100 engine, the four-valve "curtain zone" is half larger in intake and 70 percent larger in exhaust than the two-valve "curtain zone". Of course, everything has its range of application, not to say that the more valve "curtain area" value is greater, according to experts calculate when each cylinder valve increased to six, "curtain area" value will decline, and the more valve mechanism more complex, the greater the cost. Therefore, the number of valves per cylinder of the multi-valve fuel engine of the current car is three to five, of which four valves are the most common.

Take gasoline engine as an example. Compared with traditional two-valve engine, multi-valve engine can suck in more air to mix fuel for combustion, save fuel, discharge waste gas faster, emit less pollution, improve engine power and reduce noise, which is in line with the development direction of optimizing the environment and saving energy, so multi-valve technology can be rapidly popularized.

When the multi-valve fuel engine began to emerge, some people thought it had a technical defect, low speed operation is not smooth, the famous German car company Polscher held such a view. With the continuous improvement of technology, this technical defect of multi-valve gas engine has been gradually overcome. In recent years, the 944S2 of Porche Automobile Company is equipped with a four-cylinder and four-valve engine. Now, almost all the middle and senior cars in the world are equipped with multi-valve fuel engines.