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Do you really understand the engine intake and exhaust valves?

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2020.11.20 09:50:18

Do you really understand the engine intake and exhaust valves?

Valve is an important engine component. The function of the valve is to input air into the engine and exhaust the exhaust gas after combustion.

Function of intake and exhaust valves

From the engine structure, it is divided into intake and exhaust valves. The function of the intake port is to suck air into the interior of the engine and mix it with fuel for combustion; The function of the exhaust valve is to exhaust combustion exhaust gas and dissipate heat.


The function of the valve is specifically used to input fuel into the engine and exhaust gas. Traditional engines have only one air inlet and one exhaust port per cylinder. This design has a relatively simple structure, low cost, convenient maintenance, and good low speed performance. The disadvantage is that it is difficult to improve power, especially during high-speed operation, resulting in low inflation efficiency and poor performance.


Intake and exhaust valve structure

In order to improve intake and exhaust efficiency, multi valve technology is now widely used. It is common to have four valves per cylinder (there are also designs with three or five valves per cylinder, with the same principle, such as the Audi A6 engine). Four cylinders have a total of 16 valves, and the 16V we often see in automotive data means that the engine has a total of 16 valves. The multi valve structure is easy to form a compact combustion chamber, and the nozzle is arranged in the center position, which can make the combustion speed of the oil gas mixture faster and more uniform. The self weight and opening degree of each valve will also be appropriately reduced, resulting in faster valve opening and closing speed.


Engine intake and exhaust valves

The valve consists of a valve head and a stem. The valve head temperature is very high (intake valve 570-670K, exhaust valve 1050-1200K), and it also bears gas pressure, valve spring force, and inertia force of rotating components. Its lubrication and cooling conditions are poor, requiring the valve to have a certain strength, stiffness, heat resistance, and wear resistance. Alloy steel (chromium steel, nickel chromium steel) is generally used for intake valves, and heat resistant alloy (silicon chromium steel) is used for exhaust valves. Sometimes, in order to save heat resistant alloy, the exhaust valve head is made of heat resistant alloy, and the rod is welded with chromium steel.


The shapes of the valve head include a flat top, a spherical top, and a horn top. Generally, flat roofs are used. The flat top valve head has simple structure, convenient manufacturing, small heat absorption area, and small mass, and can be used for intake and exhaust valves. Spherical top air valve is a new type of exhaust valve, which has high strength, small exhaust resistance, and good smoke exhaust effect, but has large heating surface, large inertia, and complex processing. The horn type has a certain streamlined shape, which can reduce the intake resistance, but the head heating area is large, which is only suitable for the intake valve.

Engine intake and exhaust valve

The cone angle of a valve refers to the angle of the valve sealing surface, which is generally 45 degrees, and some are 30 degrees (CA1091 6102 engine). The 30 ° valve has the same lift, small valve taper, large valve end face, and small intake resistance. However, due to its small taper, thin valve head edge, small stiffness, and poor sealing and thermal conductivity, it is generally used for intake valves. The thickness of the valve body edge is generally 1~3mm to prevent the valve body from being damaged by work impact or being burnt out by high temperature. In order to reduce the intake resistance and improve the intake efficiency of the cylinders, most engine cylinders have an intake efficiency. The colors of used air intakes and exhaust valves are also different.


The valve stem is cylindrical and constantly reciprocates in the valve guide. The surface must be heat treated and polished. The shape of the valve stem end depends on the fixed form of the valve spring. The commonly used structure is to fix the spring seat with two lock halves. The end of the valve rod has a ring groove for installing a lock piece, some are fixed with a lock pin, and the end has a hole for installing the lock pin.


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