【Hundred Questions】What is the function of the engine air valve? Description of the structure and material

table of contents
The air valve is responsible for the internal regulation of the engine
What is the function of intake valve and exhaust valve?
●What changes will the size and shape of the engine air valve bring?
●Now the mainstream valve system is DOHC

Air valves are responsible for regulating the interior of the engine

The structure of a car engine is very complex, and its composition can be roughly divided into three parts.

The crankcase that supports the crankshaft and converts the reciprocating motion of the engine into rotary motion, the cylinder body that fixes the reciprocating motion of the piston, and the cylinder head that assembles the valves and valves.

The gas valve can send the mixed gas of mixed fuel and air into the combustion chamber immediately and in an appropriate amount, and discharge the combusted gas out of the combustion chamber.

What is the function of intake and exhaust valves?

Air valves are divided into intake valves and exhaust valves.

The intake valve is arranged at the intake port of the cylinder head and is responsible for sending the mixed gas into the cylinder. On the other hand, the exhaust valve is installed on the exhaust port and opens when the combustion gas in the cylinder is exhausted.

The action of the gas valve is linked with the camshaft, and the valve normally closed by the spring force will be pushed by the rotation of the camshaft to open the valve and send the mixed gas into the cylinder. After the camshaft rotates again, the valve will return to the original closed position.

What changes will the size and shape of the engine air valve bring?

At present, the "4-valve type" with 2 intake valves and 2 exhaust valves in one cylinder is the mainstream. This design method can reduce the size of the air valve, and can also achieve a lightweight effect, so that the engine can also be used at high speeds.
In addition, because the spark plug can be arranged in the center of the combustion chamber, and the gas valve is arranged around the spark plug, the spark can be evenly distributed to the combustion chamber.

Manufacturers and engineers have their own opinions on the shape and size of air valves.
For example: Some people think that to improve the efficiency of air intake and exhaust, the outer diameter of the mushroom head should be larger, the better. into the combustion chamber.
But in this way, the combustion chamber space must be enlarged and the heat dissipation is higher, so there is a disadvantage that the combustion temperature cannot be increased and it is difficult to create high output power.
Adjusting these advantages and disadvantages is also the difficulty of car engines.

In addition, the gas valve must be able to withstand the high temperature and high pressure gas in the combustion chamber and the huge impact generated by the intake and exhaust, so the gas valve must meet the requirements of impact resistance, consumption resistance and light weight.

Now the mainstream valve system is DOHC

The overall movable mechanism of the valve and camshaft is called "valve system". The placement of the valves and camshafts will greatly affect engine performance.

There are various types of valve systems, and the current mainstream is SOHC with single camshaft and DOHC with double camshaft.

SOHC is characterized by low cost, but it is not conducive to the high-speed operation of the engine; while DOHC is expensive, but it can create a high-performance engine.

Now almost all MPVs to light vehicles use DOHC engines. In the past, DOHC was a symbol of high performance. Even the "DOHC 16 valve" nameplate was installed on the rear windshield and the side of the car, which means that the car is equipped with a high-performance engine.

In the past, DOHC was regarded as a high-cost and complicated technology. Today, it has evolved into an engine that can be built with low cost and simple technology. High output power and excellent fuel consumption performance are no longer rare.

Original source:What role do engine valves play?Commentary on structure and materials
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